[libc] Fix misplaced [[noreturn]] attribute.

Summary:
This needs to go after `extern "C"`.

Author: jhuber6

libc/src/__support/OSUtil/baremetal/quick_exit.cpp

@@ -9,7 +9,7 @@
 #include "src/__support/OSUtil/quick_exit.h"
 
 // This is intended to be provided by the vendor.
-[[noreturn]] extern "C" void __llvm_libc_quick_exit(int status);
+extern "C" [[noreturn]] void __llvm_libc_quick_exit(int status);
 
 namespace LIBC_NAMESPACE {