[libc] [llvm] [libc] Remove obsolete LIBC_HAS_BUILTIN macro (PR #86554)

[Marc Auberer via llvm-commits]

================
@@ -11,7 +11,6 @@
 
 #include "include/llvm-libc-macros/math-macros.h"
 #include "src/__support/macros/attributes.h" // LIBC_INLINE
-#include "src/__support/macros/config.h"     // LIBC_HAS_BUILTIN
----------------
marcauberer wrote:

Done.

https://github.com/llvm/llvm-project/pull/86554