### Example

##### example.rb

```ruby
h = {}
(1..17).each{h[_1] = _1}
(1..16).each{h.delete(_1)}
h.rehash
```

##### ASAN report

```console
$ bin/mruby example.rb
==52587==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000006998 at pc 0x55a29cddf96b bp 0x7fff7b1b1720 sp 0x7fff7b1b1710
READ of size 4 at 0x602000006998 thread T0
    #0 0x55a29cddf96a in ib_it_next /mruby/src/hash.c:639
    #1 0x55a29cde2ca2 in ht_rehash /mruby/src/hash.c:900
    #2 0x55a29cde379f in h_rehash /mruby/src/hash.c:996
    #3 0x55a29cde7f3d in mrb_hash_rehash /mruby/src/hash.c:1735
    #4 0x55a29ce77b62 in mrb_vm_exec /mruby/src/vm.c:1451
    #5 0x55a29ce5fa88 in mrb_vm_run /mruby/src/vm.c:981
    #6 0x55a29ceb87e1 in mrb_top_run /mruby/src/vm.c:2874
    #7 0x55a29cf36bdf in mrb_load_exec mrbgems/mruby-compiler/core/parse.y:6805
    #8 0x55a29cf36f25 in mrb_load_detect_file_cxt mrbgems/mruby-compiler/core/parse.y:6848
    #9 0x55a29cdba0a2 in main /mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:347
    #10 0x7f24ef43b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #11 0x55a29cdb4a6d in _start (/mruby/bin/mruby+0x2a3a6d)

0x602000006998 is located 0 bytes to the right of 8-byte region [0x602000006990,0x602000006998)
allocated by thread T0 here:
    #0 0x7f24f01cfffe in __interceptor_realloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dffe)
    #1 0x55a29ceb9440 in mrb_default_allocf /mruby/src/state.c:68
    #2 0x55a29cdba747 in mrb_realloc_simple /mruby/src/gc.c:228
    #3 0x55a29cdba928 in mrb_realloc /mruby/src/gc.c:242
    #4 0x55a29cde12e5 in ht_init /mruby/src/hash.c:749
    #5 0x55a29cde2b8e in ht_rehash /mruby/src/hash.c:897
    #6 0x55a29cde379f in h_rehash /mruby/src/hash.c:996
    #7 0x55a29cde7f3d in mrb_hash_rehash /mruby/src/hash.c:1735
    #8 0x55a29ce77b62 in mrb_vm_exec /mruby/src/vm.c:1451
    #9 0x55a29ce5fa88 in mrb_vm_run /mruby/src/vm.c:981
    #10 0x55a29ceb87e1 in mrb_top_run /mruby/src/vm.c:2874
    #11 0x55a29cf36bdf in mrb_load_exec mrbgems/mruby-compiler/core/parse.y:6805
    #12 0x55a29cf36f25 in mrb_load_detect_file_cxt mrbgems/mruby-compiler/core/parse.y:6848
    #13 0x55a29cdba0a2 in main /mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:347
    #14 0x7f24ef43b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
```

Ruby 2.5 is the oldest maintained version.

Explicit top level task to clarify in `tasks/test.rake`

Along with some refactoring on `mruby-math` tests.

Both MinGW and MSVC provide _WIN32 macro.

`compile_as_cxx` should generate a path under` conf.build_dir`

Ignore if `conf.enable_test` does not exist

No need to check class definition

Because if the configuration file didn't contain any `conf.enable_test`, `rake test` would report an exception and exit.

```console
% cat my_config.rb
MRuby::Build.new { toolchain }

% rake MRUBY_CONFIG=my_config.rb test

  ...SNIP...

rake aborted!
NoMethodError: undefined method `invoke' for nil:NilClass
/var/tmp/mruby/tasks/test.rake:24:in `block (3 levels) in <top (required)>'
Tasks: TOP => test => test:build => test:build:lib
(See full trace by running task with --trace)
```

Because now the `Struct` class is always defined when this file is included.

If the current directory is different from `MRUBY_ROOT` and it has` conf.build_dir` and `conf.enable_cxx_exception` set, it was generating a pathname outside of` build_dir`.
As a result, in some cases files unrelated to mruby could be linked.

```console
% pwd
/tmp/mruby/1/2/3/4/5/6

% mruby_dir=/tmp/mruby/a/b/c/d/mruby

% cat my_config.rb
MRuby::Build.new("host", "build/to/custom/directory") do
  toolchain
  enable_cxx_exception
end

% rake MRUBY_CONFIG=my_config.rb -f $mruby_dir/Rakefile > logs
% grep CXX logs
CXX   a/b/c/d/mruby/src/error-cxx.cxx -> a/b/c/d/mruby/src/error-cxx.o
CXX   a/b/c/d/mruby/src/gc-cxx.cxx -> a/b/c/d/mruby/src/gc-cxx.o
CXX   a/b/c/d/mruby/src/vm-cxx.cxx -> a/b/c/d/mruby/src/vm-cxx.o
CXX   a/b/c/d/mruby/mrbgems/mruby-compiler/core/codegen-cxx.cxx -> a/b/c/d/mruby/mrbgems/mruby-compiler/core/codegen-cxx.o
CXX   a/b/c/d/mruby/mrbgems/mruby-compiler/core/y.tab-cxx.cxx -> a/b/c/d/mruby/mrbgems/mruby-compiler/core/y.tab-cxx.o
CXX   ../a/b/c/d/mruby/src/error-cxx.cxx -> ../a/b/c/d/mruby/src/error-cxx.o
CXX   ../a/b/c/d/mruby/src/gc-cxx.cxx -> ../a/b/c/d/mruby/src/gc-cxx.o
CXX   ../a/b/c/d/mruby/src/vm-cxx.cxx -> ../a/b/c/d/mruby/src/vm-cxx.o
```

Exclude `<build-dir>/mrbc/**/*` from rake target rules

Make the argument of `Kernel#catch` optional as Ruby does

Prevents the auto-generated mrbc target source code from being compiled under host conditions.

This is because a build error occurred when `conf.enable_cxx_exception` was set.

Also implement the following changes.

* Add tests
* Use `Object#equal?` to compare tags for Ruby compatibility
* Use `attr_reader`

Fix message of `ThrowCatchJump` in `mruby-catch` gem

* Use `_Complex` instead of `complex` (MSYS2 do not support `complex`)
* Use `_Dcomplex` instead of `_Complex` on MSCV
* Avoid operator division and multiplication of complex

### Example

```ruby
begin
  throw 1
rescue Exception => e
  puts e.message
end
```

#### Before this patch:

```console
$ bin/mruby example.rb
uncaught throw :1
```
#### After this patch (same as Ruby):

```console
$ bin/mruby example.rb
uncaught throw 1
```

This gem uses C99 `_Complex` features. You need a C compiler that
supports `_Complex` to enable this gem. All `gcc`, `clang`, `VC` support
`_Complex` so there should not be a big problem.

* Use `class_eval` instead of `instance_eval`.
* Reduce `class_eval` calls
* define `Numeric#i`
* undefine `Complex#i`

Check if `.pi` build rules are defined

`.pi` files are created for `.o` files that `build.products` depends on, but
an error will occur if the build rule is unknown, so add a check.

I don't think this situation would normally arise. However, in
`mattn/mruby-onig-regexp`, when using bundled onigmo, onigmo's `.o` files
are added to dependency of `libmruby.a` in the second and subsequent builds,
and mruby does not know the build rule, so the following error had occured.

```console
rake aborted!
Don't know how to build task '/mruby/build/host/mrbgems/mruby-onig-regexp/onigmo-6.2.0/libonig_objs/ascii.pi' (See the list of available tasks with `rake --tasks`)
```

Fix breakage where builds except `host` don't refer` mrbc` in `host`

Build error occurred under the following conditions.

* `host` build is presym enabled and unspecified `mruby-bin-mrbc` gem.
* Build except `host` unspecified `mruby-bin-mrbc` gem and mrbcfile.

### Example

#### Build configuration

```ruby
MRuby::Build.new{|conf| conf.toolchain}
MRuby::Build.new("host2"){|conf| conf.toolchain}
```

#### Error

```console
rake aborted!
external mrbc or mruby-bin-mrbc gem in current('host2') or 'host' build is required
/mruby/lib/mruby/build.rb:326:in `mrbcfile'
/mruby/tasks/mrblib.rake:9:in `block in <top (required)>'
/mruby/lib/mruby/build.rb:18:in `instance_eval'
/mruby/lib/mruby/build.rb:18:in `block in each_target'
/mruby/lib/mruby/build.rb:17:in `each'
/mruby/lib/mruby/build.rb:17:in `each_target'
/mruby/tasks/mrblib.rake:1:in `<top (required)>'
/mruby/Rakefile:27:in `load'
/mruby/Rakefile:27:in `<top (required)>'
```

We don't want to increase number of files that should be compiled by C++
compiler when `enable_cxx_exception` is turned on.