Define a Wasm global to store pthread_self

Author: abrown

libc-top-half/musl/src/thread/pthread_self.c

@@ -1,6 +1,12 @@
 #include "pthread_impl.h"
 #include <threads.h>
 
+#if defined(_REENTRANT)
+// We need some place to store the thread ID. This WebAssembly global fits the
+// bill and is used by `__get_tp` elsewhere.
+__asm__(".globaltype __wasilibc_pthread_self, i32\n");
+#endif
+
 static pthread_t __pthread_self_internal()
 {
 	return __pthread_self();