[llvm] [libc][bazel] Mark socket functions weak (PR #115088)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

> Is there any reason why we shouldn't just define all libc functions as "weak"?

Note that declaring a function as having `weak` linkage is an optimization barrier that inhibits inter-proceedural optimizations such as inlining and constant propagation.  If downstream users ever hope to LTO llvm-libc, then marking everything as weak will prevent such optimizations.

https://github.com/llvm/llvm-project/pull/115088