x86: Fix breakage of UML from the changes in the rwsem system

The patches 5d0b7235d8 and
bafaecd11d broke the UML build:

On Sun, 17 Jan 2010, Ingo Molnar wrote:
>
> FYI, -tip testing found that these changes break the UML build:
>
> kernel/built-in.o: In function `__up_read':
> /home/mingo/tip/arch/x86/include/asm/rwsem.h:192: undefined reference to `call_rwsem_wake'
> kernel/built-in.o: In function `__up_write':
> /home/mingo/tip/arch/x86/include/asm/rwsem.h:210: undefined reference to `call_rwsem_wake'
> kernel/built-in.o: In function `__downgrade_write':
> /home/mingo/tip/arch/x86/include/asm/rwsem.h:228: undefined reference to `call_rwsem_downgrade_wake'
> kernel/built-in.o: In function `__down_read':
> /home/mingo/tip/arch/x86/include/asm/rwsem.h:112: undefined reference to `call_rwsem_down_read_failed'
> kernel/built-in.o: In function `__down_write_nested':
> /home/mingo/tip/arch/x86/include/asm/rwsem.h:154: undefined reference to `call_rwsem_down_write_failed'
> collect2: ld returned 1 exit status

Add lib/rwsem_64.o to the UML subarch objects to fix.

LKML-Reference: <alpine.LFD.2.00.1001171023440.13231@localhost.localdomain>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/um/sys-x86_64/Makefile

@@ -8,7 +8,8 @@ obj-y = bug.o bugs.o delay.o fault.o ldt.o mem.o ptrace.o ptrace_user.o \
 	setjmp.o signal.o stub.o stub_segv.o syscalls.o syscall_table.o \
 	sysrq.o ksyms.o tls.o
 
-subarch-obj-y = lib/csum-partial_64.o lib/memcpy_64.o lib/thunk_64.o
+subarch-obj-y = lib/csum-partial_64.o lib/memcpy_64.o lib/thunk_64.o \
+		lib/rwsem_64.o
 subarch-obj-$(CONFIG_MODULES) += kernel/module.o
 
 ldt-y = ../sys-i386/ldt.o