[MIPS] Add __cmpdi2

Certain 32-bit kernel configurations seem to be able to cause references,
this was observed with gcc 4.1.2.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/lib/Makefile

@@ -28,4 +28,4 @@ obj-$(CONFIG_CPU_TX49XX)	+= dump_tlb.o
 obj-$(CONFIG_CPU_VR41XX)	+= dump_tlb.o
 
 # libgcc-style stuff needed in the kernel
-obj-y += ashldi3.o ashrdi3.o lshrdi3.o ucmpdi2.o
+obj-y += ashldi3.o ashrdi3.o cmpdi2.o lshrdi3.o ucmpdi2.o

arch/mips/lib/cmpdi2.c

+#include <linux/module.h>
+
+#include "libgcc.h"
+
+word_type __cmpdi2(long long a, long long b)
+{
+	const DWunion au = {
+		.ll = a
+	};
+	const DWunion bu = {
+		.ll = b
+	};
+
+	if (au.s.high < bu.s.high)
+		return 0;
+	else if (au.s.high > bu.s.high)
+		return 2;
+
+	if ((unsigned int) au.s.low < (unsigned int) bu.s.low)
+		return 0;
+	else if ((unsigned int) au.s.low > (unsigned int) bu.s.low)
+		return 2;
+
+	return 1;
+}
+
+EXPORT_SYMBOL(__cmpdi2);