[libcxx] [llvm] [libc++] Add support for picolibc and newlib in RUNTIMES_USE_LIBC (PR #147956)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

> Do you see any failures or other issues related to the checks?

No, just noticed that there are a couple more places where the new option/define could be used.


https://github.com/llvm/llvm-project/pull/147956