um: fix strrchr() problems

richard@nod.at:
Fixes:
  /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/libc.a(strrchr.o): In function `rindex':
  (.text+0x0): multiple definition of `strrchr'

If both STATIC_LINK and UML_NET_VDE are set to "y" libc's strrchr may
clash with the kernel implementation.

This workaround comes originally from Jeff Dike:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=494995#35

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/Makefile

@@ -41,7 +41,7 @@ KBUILD_CPPFLAGS += -I$(srctree)/$(ARCH_DIR)/sys-$(SUBARCH)
 KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ -DSUBARCH=\"$(SUBARCH)\" \
 	$(ARCH_INCLUDE) $(MODE_INCLUDE) -Dvmap=kernel_vmap	\
 	-Din6addr_loopback=kernel_in6addr_loopback \
-	-Din6addr_any=kernel_in6addr_any
+	-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr
 
 KBUILD_AFLAGS += $(ARCH_INCLUDE)