http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=494995
Fix symbol clash between libc and the kernel.

--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -93,7 +93,8 @@
 # defines more robust
 
 KERNEL_DEFINES = $(strip -Derrno=kernel_errno -Dsigprocmask=kernel_sigprocmask \
-			 -Dmktime=kernel_mktime $(ARCH_KERNEL_DEFINES))
+			 -Dmktime=kernel_mktime -Dstrrchr=kernel_strrchr \
+			 $(ARCH_KERNEL_DEFINES))
 KBUILD_CFLAGS += $(KERNEL_DEFINES)
 
 PHONY += linux