[PATCH] Rename to `struct rbimpl_size_overflow_tag`

	This struct is used for addition not only for multiplication, so
	remove the word `mul`, and make the member names more descriptive.

	[PATCH] Move rbimpl_size_add_overflow from gc.c to memory.h

	[PATCH] Remove rbimpl_rstring_getmem() usage as workaround for GCC 15.2.1 optimization bug. [Bug #21655]

	[PATCH] include/ruby/internal/core/rstring.h: Remove rbimpl_rstring_getmem() definition.

	[PATCH] simplify RSRING_GETMEM() definition.

	[PATCH] [Bug #21629] Initialize `struct RString`

which appears to be missed in the previous commit for some reason.

	[PATCH] Add `RBIMPL_ATTR_NONSTRING_ARRAY()` macro for GCC 15

	[PATCH] [Bug #21629] Enable `nonstring` attribute on clang 21

	[PATCH] [Bug #21629] Initialize `struct RString`

	[PATCH] [Bug #21629] Initialize `struct RArray`

	Suppress gcc 15 unterminated-string-initialization warnings

	Separate `__has_attribute` from `defined(__has_attribute)`

	Fix Visual C warnings:
	```
	regenc.h(121): warning C4067: unexpected tokens following preprocessor directive - expected a newline
	```

	Cast up `int` instruction code to `VALUE`

	Fix Visual C warnings:
	```
	iseq.c(3793): warning C4312: 'type cast': conversion from 'int' to 'void *' of greater size
	iseq.c(3794): warning C4312: 'type cast': conversion from 'int' to 'void *' of greater size
	```

	Do not let files depend on a phony target

	Detect `clock_gettime` and `clock_getres` for winpthreads

As reported in <https://bugs.ruby-lang.org/issues/21340>, older autoconf
have an AC_HEADER_STDBOOL that's incompatible with C23. Autoconf 2.72
fixed the macro, but also mentions that it's obsolescent since all
current compilers have this header.

Since we require C99 [1] and VS 2015 [2], should be able take
that suggestion and include stdbool.h without a check. This worked
fine on rubyci.org.

[Backport #21340]

[1]: https://bugs.ruby-lang.org/issues/15347
[2]: https://bugs.ruby-lang.org/issues/19982

	Fix redefinition of `clock_gettime` and `clock_getres`

	winpthreads-git 12.0.0.r720 provides `clock_gettime` and
	`clock_getres` as inline functions.

	digest.so needs ruby/digest.h which is installed by build-ext

	Copy to path with the base name

Backport [Bug #21286]

And finally deprecated at C++-17.
Patched by jprokop (Jarek Prokop).