[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
+# RUNTIMES_USE_LIBC was checked in HandleLibC to be one of accepted values
+if (RUNTIMES_USE_LIBC STREQUAL "llvm-libc")
+  set(LIBCXX_LIBC_LLVMLIBC 1)
+elseif (RUNTIMES_USE_LIBC STREQUAL "picolibc")
+  set(LIBCXX_LIBC_PICOLIBC 1)
+  # picolibc is derived from newlib and behaves the same in regards to libc++
+  # so setting both here:
+  # * LIBCXX_LIBC_NEWLIB is used now
+  # * LIBCXX_LIBC_PICOLIBC can be used for further customizations later
+  set(LIBCXX_LIBC_NEWLIB 1) 
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voltur01 wrote:

It was for completeness only - removed now.

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