[S390]: Fix build on 31-bit.

Allow s390 to properly override the generic
__div64_32() implementation by:

1) Using obj-y for div64.o in s390's makefile instead
   of lib-y

2) Adding the weak attribute to the generic implementation.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/s390/lib/Makefile

@@ -5,6 +5,6 @@
 EXTRA_AFLAGS := -traditional
 
 lib-y += delay.o string.o uaccess_std.o uaccess_pt.o qrnnd.o
-lib-$(CONFIG_32BIT) += div64.o
+obj-$(CONFIG_32BIT) += div64.o
 lib-$(CONFIG_64BIT) += uaccess_mvcos.o
 lib-$(CONFIG_SMP) += spinlock.o

arch/s390/lib/div64.c

@@ -147,5 +147,3 @@ uint32_t __div64_32(uint64_t *n, uint32_t base)
 }
 
 #endif /* MARCH_G5 */
-
-EXPORT_SYMBOL(__div64_32);

lib/div64.c

@@ -23,7 +23,7 @@
 /* Not needed on 64bit architectures */
 #if BITS_PER_LONG == 32
 
-uint32_t __div64_32(uint64_t *n, uint32_t base)
+uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
 {
 	uint64_t rem = *n;
 	uint64_t b = base;