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

Run test-bundled-gems-run and test-bundled-gems-spec sequentially.

This reverts commit 5a332940ed2f809cb17af7e4d068089b6e1fa6ca.
Something does not work well on Github Actions.

Not to build the rubyspec-capiext extension libraries again on the
next build after the build all extensions get built, ensure these
extensions are up to date when recursively building from exts.mk.

Colons are special in Makefiles.

By replacing `ALLOBJS` suffix with intermediate file suffixes instead
of roughly removing by wildcards.  Made `cleanlibs` append `.dSYM`
suffix for each word in `TARGET_SO`, not the end of the entire list.