[libc] Make headers compatible with C++ < 11 (llvm#123260)

C++11 introduced `noexcept`, but `throw()` can be used in older
versions of the language.

Author: frobtech

libc/include/__llvm-libc-common.h

@@ -39,7 +39,11 @@
 #define _Thread_local thread_local
 
 #undef __NOEXCEPT
+#if __cplusplus >= 201103L
 #define __NOEXCEPT noexcept
+#else
+#define __NOEXCEPT throw()
+#endif
 
 #else // not __cplusplus