runtime: fix libunwind to compatible with homebrew linux

runtime/internal/clite/debug/_wrap/debug.c

@@ -1,6 +1,8 @@
 #if defined(__linux__)
 #define UNW_LOCAL_ONLY
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #include <features.h>
 #endif
 

runtime/internal/clite/debug/debug.go

@@ -11,8 +11,8 @@ import (
 )
 
 const (
-	LLGoPackage = "link"
-	LLGoFiles   = "_wrap/debug.c"
+	LLGoPackage = "link: $(llvm-config --ldflags --libs); -lunwind"
+	LLGoFiles   = "$(llvm-config --cflags): _wrap/debug.c"
 )
 
 type Info struct {