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

[Volodymyr Turanskyy via llvm-commits]

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@@ -481,6 +481,21 @@ include(config-ix)
 include(HandleLibC) # Setup the C library flags
 include(HandleLibCXXABI) # Setup the ABI library flags
 
+# Set C library in use to define respective macro in __config_site
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voltur01 wrote:

Thank you for review!

Good point, moved and made use of config_define() for consistency.

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