nios2: fix r15 issue for gcc4

The "-ffixed-r15" option doesn't work well for gcc4. Since we
don't use gp for small data with option "-G0", we can use gp
as global data pointer. This allows compiler to use r15. It
is necessary for gcc4 to work properly.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Signed-off-by: Scott McNutt <smcnutt@psyent.com>
diff --git a/examples/standalone/stubs.c b/examples/standalone/stubs.c
index ce3371d..0187708 100644
--- a/examples/standalone/stubs.c
+++ b/examples/standalone/stubs.c
@@ -84,7 +84,7 @@
 	: : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x) : "r0");
 #elif defined(CONFIG_NIOS2)
 /*
- * r15 holds the pointer to the global_data, r8 is call-clobbered
+ * gp holds the pointer to the global_data, r8 is call-clobbered
  */
 #define EXPORT_FUNC(x) \
 	asm volatile (			\
@@ -92,11 +92,11 @@
 #x ":\n"				\
 "	movhi	r8, %%hi(%0)\n"		\
 "	ori	r8, r0, %%lo(%0)\n"	\
-"	add	r8, r8, r15\n"		\
+"	add	r8, r8, gp\n"		\
 "	ldw	r8, 0(r8)\n"		\
 "	ldw	r8, %1(r8)\n"		\
 "	jmp	r8\n"			\
-	: : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x * sizeof(void *)) : "r15");
+	: : "i"(offsetof(gd_t, jt)), "i"(XF_ ## x * sizeof(void *)) : "gp");
 #elif defined(CONFIG_M68K)
 /*
  * d7 holds the pointer to the global_data, a0 is a call-clobbered