[libc] mark internal definitions as nothrow

[nickdesaulniers]

Forked from #112415.

Most of our internal declarations (example: headers under libc/src/) do not have the gnu::nothrow function attribute on the declarations or definitions. We should probably add them.

https://gcc.gnu.org/onlinedocs/gcc-4.5.3/gcc/Function-Attributes.html

most functions in the standard C library can be guaranteed not to throw an exception with the notable exceptions of qsort and bsearch that take function pointer arguments.

[llvmbot]

@llvm/issue-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Forked from https://github.com//pull/112415.

Most of our internal declarations (example: headers under libc/src/) do not have the gnu::nothrow function attribute on the declarations or definitions. We should probably add them.

https://gcc.gnu.org/onlinedocs/gcc-4.5.3/gcc/Function-Attributes.html

> most functions in the standard C library can be guaranteed not to throw an exception with the notable exceptions of qsort and bsearch that take function pointer arguments.