[libc] Update C symbols aliasing function declarations.

[lntue]

No description provided.

[nickdesaulniers]

For my fullbuild with clang, for each of the functions modified in this patch, I observe the following build errors:

/android0/llvm-project/libc/src/stdlib/bsearch.cpp:16:7: error: 'bsearch' is missing exception specification 'throw()'
   16 | void *bsearch(const void *key, const void *array, size_t array_size,
      |       ^
   17 |               size_t elem_size, int (*compare)(const void *, const void *)) {
      |                                                                             throw()
/android0/llvm-project/libc/src/stdlib/bsearch.h:18:26: note: previous declaration is here
   18 | LIBC_FUNCTION_DECL void *bsearch(const void *key, const void *array,
      |                          ^

[nickdesaulniers]

If there's only 1 expression, prefer ifdef over if defined.