[PATCH] [Bug #21779] Uniquify `InitVM` functions as well as `Init`

	Avoid possible name conflict when `--with-static-linked-ext`.

	[PATCH] [Bug #21779] Do not export InitVM functions

	Fix ruby/io-console#105.

	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

	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

Such as `$(ruby_version)`, `$(arch)` and so on.

We have name fragmentation for this feature, including "shared GC",
"modular GC", and "external GC". This commit standardizes the feature
name to "modular GC" and the implementation to "GC library".

As common.mk is used by nmake.exe, the commands there need to be
accepted also by cmd.exe.