[libc++] Add a thread-safe version of std::lgamma in the dylib (#153631)

Libc++ currently redeclares ::lgamma_r on platforms that provide it.
This causes issues when building with modules, and redeclaring functions
provided by another library (here the C library) is bad hygiene.

Instead, use an asm declaration to call the right function without
having to redeclare it.

GitOrigin-RevId: 09d7b890e035c8ace45642f27edc0ff5768311eb