* include/grub/symbol.h (EXT_C) [!ASM_FILE]: Redefine with strings.

* grub-core/lib/i386/backtrace.c (grub_backtrace): Use EXT_C.

include/grub/symbol.h

@@ -26,9 +26,14 @@
 
 /* Add an underscore to a C symbol in assembler code if needed. */
 #ifndef GRUB_UTIL
+
 #if HAVE_ASM_USCORE
+#ifdef ASM_FILE
 # define EXT_C(sym)	_ ## sym
 #else
+# define EXT_C(sym)	"_" sym
+#endif
+#else
 # define EXT_C(sym)	sym
 #endif