Use builtins for overflow math if possible

Suppress warnings generated by -Wwrite-strings

Here are suppressed warnings:

    src/fmt_fp.c: In function 'fmt_fp':
    src/fmt_fp.c:124:16: warning: initialization discards 'const' qualifier from pointer target type
         char *ss = (t&32)?"inf":"INF";
                    ^
    src/fmt_fp.c:125:17: warning: assignment discards 'const' qualifier from pointer target type
         if (y!=y) ss=(t&32)?"nan":"NAN";
                     ^
    mrbgems/mruby-string-ext/src/string.c: In function 'mrb_str_succ_bang':
    mrbgems/mruby-string-ext/src/string.c:302:27: warning: assignment discards 'const' qualifier from pointer target type
           if (e == b) prepend = "1";
                               ^
    mrbgems/mruby-string-ext/src/string.c:305:27: warning: assignment discards 'const' qualifier from pointer target type
           if (e == b) prepend = "a";
                               ^
    mrbgems/mruby-string-ext/src/string.c:308:27: warning: assignment discards 'const' qualifier from pointer target type
           if (e == b) prepend = "A";
                               ^
    mrbgems/mruby-bin-mruby/tools/mruby/mruby.c: In function 'main':
    mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:213:13: warning: assignment discards 'const' qualifier from pointer target type
         cmdline = args.cmdline ? args.cmdline : "-";
                 ^
    mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c: In function 'print_breakpoint':
    mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c:159:3: warning: initialization discards 'const' qualifier from pointer target type
       char* enable_letter[] = {BREAK_INFO_MSG_DISABLE, BREAK_INFO_MSG_ENABLE};
       ^
    mrbgems/mruby-bin-debugger/tools/mrdb/cmdbreak.c:159:3: warning: initialization discards 'const' qualifier from pointer target type

Fix to avoid warning

Add test of negative arguments for Integer#%

fix maximum value of the index when access breakpoints.

remove unnecessary <inttypes.h> inclusion

MSVC 2015 implements inline keyword

The format specifier macros were needed to portably print a mrb_int,
because mrb_raisef() originally called vsnprintf(). It doesn't anymore
since 18b2683b and the mrb_int format
specifier macros are already gone.

Apparently the C compiler of Visual Studio 2015 CTP6 finally implements
inline as inline and not only as _inline and __inline.

mruby-time: call ISO C11's timespec_get() if available

refactor write_pool_block()

No need to write the same assertion in each case (except the default
one). Instead we can assert after the switch statement.

gettimeofday() is an obsolescent POSIX function which may be removed in
a future version. POSIX recommends using clock_gettime() (also POSIX)
instead, but it isn't available on OS X or Windows (at least with MSVC
and older MinGW versions).

Whereas timespec_get() is part of ISO C11 and mruby uses some small
other C11 features too. It isn't universally available yet either, but
it might be in the future. And Visual C++ 2015 implements it! Since
mruby strives for ISO C and not POSIX compatibility, I think it's a
reasonable choice.

TIME_UTC is used instead of __STDC_VERSION__, because if TIME_UTC is
defined, then most likely timespec_get() is too. This isn't true in case
of  __STDC_VERSION__ (see MSVC).

Fix exceptions for visualcpp

I modified the undefined frexpl in cygwin of make

Fix #2739 stack_extend in mrb_f_send

mrb_f_send needs stack_extend like OP_SEND
Signed-off-by: Go Saito <gos@iij.ad.jp>

Use ptrdiff_t to suppress signedness warning

3df32161 says so but there is no warning
with GCC 4.9 on my Debian GNU/Linux environment.

delete prototypes of undefined functions

Fix a crash bug on raising after realloc

The following program reproduces this problem:

    #include <mruby.h>

    static mrb_value
    recursive(mrb_state *mrb, mrb_value self)
    {
      mrb_int n;

      mrb_get_args(mrb, "i", &n);

      if (n == 0) {
        mrb_raise(mrb, E_RUNTIME_ERROR, "XXX");
      } else {
        mrb_funcall(mrb, self, "recursive", 1, mrb_fixnum_value(n - 1));
      }

      return self;
    }

    int
    main(void)
    {
      mrb_state *mrb;

      mrb = mrb_open();

      mrb_define_method(mrb, mrb->kernel_module, "recursive", recursive,
                        MRB_ARGS_REQ(1));
      mrb_funcall(mrb, mrb_top_self(mrb), "recursive", 1, mrb_fixnum_value(30));

      mrb_close(mrb);
    }

Recursive method call isn't required. It's just for expanding call info
stack.

If mrb_realloc() is called in cipush(), cibase address is changed. So,
we shouldn't compare ci before mrb_realloc() and cibase after
mrb_realloc(). It accesses unknown address and causes crash.

Fix a bug that no expression case doesn't return valid value

Here is a script that reproduces this problem:

     x = case
         when true; 1
         end
     p x # => main # 1 is expected

Fix a bug that if and no return value case can't return true clause value