x86, build: Don't get confused by local symbols

x86, build: Don't get confused by local symbols

arch/x86/crypto/sha1_avx2_x86_64_asm.S introduced _end as a local
symbol, which broke the build under certain circumstances.  Although
the wisdom of _end as a local symbol can definitely be questioned, the
build should not break for that reason.

Thus, filter the output of nm to only get global symbols of
appropriate type.

Reported-by: Andy Lutomirski <[email protected]>
Cc: Chandramouli Narayanan <[email protected]>
Cc: Herbert Xu <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]