[Bug #21626]

	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

We should use the rb_gc_enable/rb_gc_disable_no_rest APIs instead of
directly setting the ruby_disable_gc variable.

This reverts commit 054a412d540e7ed2de63d68da753f585ea6616c3.
SIGCHLD `waidpid`, `waitpid_lock` and related code, have been removed
at ruby/ruby#7527.

On Linux, `siginfo_t` uses a union for each `si_code`, and the field
corresponding to `si_pid` does not belong to the `_sigfault` field for
SIGSEGV.  It actually overlaps the `si_addr` field, which is usually
non-zero on stack overflow.

https://github.com/ruby/ruby/pull/10201#issuecomment-2034723244

Previously, when another process sends a fatal signals such as SIGBUS
to Ruby, we could mis-interpret it as a stack overflow Ruby itself
generated. When the si_pid field is set on the signal, we shouldn't
check the si_addr field to check for stack overflow.

> Signals sent with kill(2) and sigqueue(3) fill in si_pid and si_uid.

Co-authored-by: Alan Wu <alanwu@ruby-lang.org>

[Feature #16495]

Previously the code assigns `handler` function pointer, which accepts
one argument, to `sigact.sa_sigaction`, which accepts three argument.
This mismatch is not allowed in Wasm.

I don't see the reason to use `sa_sigaction` here, so this change
assigns to `sa_handler`, which accepts one argument, in Wasm.

3c471149910d79745b50389c436f0ed2973e0d91 added a call to `reset_sigmask`
but the guard condition didn't match with the condition used to define
`reset_sigmask`.