Remove unnecessary configuration macros; ref #5060

The following macros will be removed:
- `ENSURE_STACK_INIT_SIZE`
- `RESCUE_STACK_INIT_SIZE`
- `MRB_ECALL_DEPTH_MAX`

Change `.o.d` back to `.d` because `.pi.d` is no longer created

Build internal mrbc in an internal directory

Fixed `String#unpack` to handle the highest range of integer values

This is a correction based on the review by @matz.
https://github.com/mruby/mruby/pull/5306#pullrequestreview-578378401

Previously, problems occurred when the `fixnum` was exceeded.

- 32-bit cpu mode with `MRB_WORD_BOXING` and `MRB_INT32`:

  ```console
  % bin/mruby -e 'p [0x7fffffff].pack("N").unpack("N")'
  trace (most recent call last):
  -e:1: cannot unpack to Integer: 2147483647 (RangeError)
  ```

- 64-bit cpu mode with `MRB_WORD_BOXING` and `MRB_INT64`:

  ```console
  % bin/mruby -e 'p [0x7fffffff_ffffffff].pack("q").unpack("q")'
  trace (most recent call last):
  -e:1: cannot unpack to Integer: 9223372036854775807 (RangeError)
  ```

Raise SystemStackError if mruby VM stack expansion fails

Check first `0` when converting symbols into strings

This was because it caused `SIGSEGV` when `mruby -v` displayed an unnamed variable.

```console
% bin/mruby -ve 'call { |(a, b)| }'

  ...SNIP...

irep 0x8007d0050 nregs=3 nlocals=1 pools=0 syms=1 reps=1 iseq=12
file: -e
    1 000 OP_LOADSELF   R1
    1 002 OP_BLOCK      R2      I(0:0x8007d00a0)
    1 005 OP_SENDB      R1      :call   0
    1 009 OP_RETURN     R1
    1 011 OP_STOP

irep 0x8007d00a0 nregs=6 nlocals=5 pools=0 syms=0 reps=0 iseq=29
local variable names:
zsh: segmentation fault (core dumped)  bin/mruby -ve 'call { |(a, b)| }'
```

Refine `preprocess_options`; ref d95ffb03

If we modify an option that may have been specified by users, we may
make unintended changes, so it is better not to modify it as much as
possible, IMO.

It's for internal use. Please use `conf.disable_presym`.

Split `presym_table` for reduced program size

Because a structure that is an element of `presym_table` has padding, split
it into individual arrays for name and length.

#### Result (64-bit CPU with full-core gembox)

|        |   mruby    | libmruby.a |
|--------|------------|------------|
| Before | 1,087,444B | 1,476,872B |
| After  | 1,079,340B | 1,469,784B |

Rename `.i` created for presym scan to `.pi`

This is because compiler's `-save-temps=obj` option creates `.i` with the
same name.

Fix typos in `mruby/presym/{disable,enable}.h` [ci skip]

Avoid 'possible loss of data' casting in binary search

Fix "Use `MRB_SYM()` for error class retrieval"; ref 2ddfd50d

Because it may not be expected result.
example: https://wandbox.org/permlink/F5Mp7IEJ1VY3CFLp

The new macro (`MRB_E_SYM`) was not being used, so it is being used. Also
`MRB_E_SYM` is confusing with `MRB_SYM_E`, so change it to `MRB_ERROR_SYM`.

This reverts commit 34f82f24.
Ref #5282