#### Before this patch:
```ruby
__send__ #=> wrong number of arguments
{}.default(1,2) #=> wrong number of arguments
```
#### After this patch:
```ruby
__send__ #=> wrong number of arguments (given 0, expected 1+)
{}.default(1,2) #=> wrong number of arguments (given 2, expected 0..1)
```
Union initialization initializes the first member. The first member of
`RVALUE` is `struct free_obj`, but because it is only 4-words, it seems that
initialization after the 5th word is not ensured.
Therefore, I created 6-words `struct RVALUE_initializer` for initialization
and made it the first member.
Module#include and Module#prepend now affect classes and modules
that have already included or prepended the receiver, mirroring the
behavior if the arguments were included in the receiver before
the other modules and classes included or prepended the receiver.
```ruby
class C; end
module M1; end
module M2; end
C.include M1
M1.include M2
p C.ancestors #=> [C, M1, M2, Object, Kernel, BasicObject]
```
Due to the above changes, it may not work with the existing build
configurations in cross-compilation (even if we can build without presym),
therefore revert it once (ref https://github.com/mruby/mruby/pull/5202#issuecomment-735412643). Sorry for the lack of consideration.
Currently, the size of writing in heap by write_irep_record() is
bigger than The size that is calculated by get_irep_record_size.
Therefore, irep is dumped over the size of allocating memory when we
execute dump_irep().
Previously, presym files were always created in `build/{presym,presym.inc}`.
However, this constraint is inconvenient because it is common to use
multiple build configurations and build targets in a single mruby tree.
Therefore, change to create presym file for each build target.
Jump target address is `operand (16bit)` + `address of next instruction`.
In addition, `ilen` was made `uint32_t` so that `iseq` length limitation
of 65536 is removed. Only jump target address should be within signed
16bit (-32768 .. 32767).
Chang to compare string length first.
### Benchmark
#### Code
* https://github.com/shuujii/mruby-presym_find-benchmark
#### Result
```console
Previous: 10.240772M i/s (25M times in 2.441222s)
New: 16.412985M i/s (25M times in 1.523184s)
```
Integrate the implementation with `Module#define_method`.
- Introduce the internal function `mrb_mod_define_method_m()` (no static)
- The `Object#define_singleton_method` method can now accept a second argument
KOBAYASHI Shuji