[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`

See <https://bugs.ruby-lang.org/issues/19417#note-3>.

https://unicode.org/reports/tr18/#word states word should match join_control chars.

It did not previously:

```ruby
[*0x0..0xD799, *0xE000..0x10FFFF].map { |n| n.chr 'utf-8' } => all_chars
all_chars.grep(/\p{join_control}/) => jc
jc.count # => 2
jc.grep(/\p{word}/).count # => 0
```
[Backport #19417]

---

Backporting note: I regenerated `enc/unicode/15.0.0/name2ctype.h` using
`make update-unicode`.

	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

Include € euro sign from CCSID 864

Co-Authored-by: lish82 (Hiroki Katagiri)