clang > 20.1.4 compat: unterminated strings

[Lukasdoe]

clang introduced a new warning (following gcc) for string initialization to char arrays that do not fit the null terminal.

Introduced here: llvm/llvm-project#137829
Included in LLVM version LLVM 20.1.4+

More detail:
-Wunterminated-string-initialization warns for c string literals that are written to a buffer too small to include a null terminator. This warning is also included in -Wextra which is enabled for wasi-libc and fails compilation due to -Werror.

Possible fixes:

1. deactivate the warning
2. add __attribute__ ((nonstring)) to the three occurrences where this is a problem.

Chosen solution: 1.
Since the attribute is not available on older clang versions, it would trigger another warning there.

(included a small formatting change in the commit - pls ignore)

[yamt]

Since the attribute is not available on older clang versions, it would trigger another warning there.

have you considered __has_attribute?

[Lukasdoe]

I did not! However, applying the __has_attribute macro would introduce an ifdef, cluttering the code. Idk what is best in this situation tbh, since it's only 3 sites in the entire project that trigger the warning. What would you suggest ist a cleaner solution?

[yamt]

the three occurrences where this is a problem.

for those who wonder where they are:

libc-top-half/musl/src/stdio/vfprintf.c:170:2: warning: initializer-string for character array is too long, array size is 16 but initializer has size 17 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Wunterminated-string-initialization]
  170 |         "0123456789ABCDEF"
      |         ^~~~~~~~~~~~~~~~~~
libc-top-half/musl/src/locale/pleval.c:90:31: warning: initializer-string for character array is too long, array size is 11 but initializer has size 12 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Wunterminated-string-initialization]
   90 |         static const char opch[11] = "|&=!><+-*%/";
      |                                      ^~~~~~~~~~~~~
libc-top-half/musl/src/locale/pleval.c:91:31: warning: initializer-string for character array is too long, array size is 6 but initializer has size 7 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Wunterminated-string-initialization]
   91 |         static const char opch2[6] = "|&====";
      |                                      ^~~~~~~~

[sbc100]

Hmm.. I wonder if we should be compiling musl with -Wextra -Werror at all? I suppose the list of exception is manageable right now but if it starts to grow we should probably just drop the -Wextra since its not something that upstream musl builds with.