[compiler-rt] don't use mallopt on musl (PR #101055)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Perhaps we should just remove `mallopt`. Other sanitizers don't use `mallopt`. musl doesn't provide `mallopt`. tcmalloc ignores `mallopt`. Param 1 conflicts with Android `M_INIT_ZYGOTE_CHILD_PROFILING`

https://github.com/llvm/llvm-project/pull/101055