Modify attributes.h to use new LIBC_THREAD_MODE

Author: saturn691

libc/src/__support/macros/attributes.h

@@ -28,7 +28,9 @@
 #define LIBC_INLINE_ASM __asm__ __volatile__
 #define LIBC_UNUSED __attribute__((unused))
 
-#ifdef LIBC_TARGET_ARCH_IS_GPU
+// LIBC_THREAD_MODE is undefined when building libcxx. However, it is ok to just
+// use thread_local in a C++ context
+#if defined(LIBC_THREAD_MODE) && LIBC_THREAD_MODE == LIBC_THREAD_MODE_SINGLE
 #define LIBC_THREAD_LOCAL
 #else
 #define LIBC_THREAD_LOCAL thread_local