Bug 338615 suppress glibc 2.20 optimized strcmp implementation for ARMv7.

Add an add_hardwired_spec for strcmp in VG_(redir_initialise) for
ld-linux.so.3 and ld-linux-armhf.so.3 to use a simple strcmp
implementation in m_trampoline.S (compiled from the trivial .c code
to asm with gcc like the other implementations in that file).

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14374 a5019735-40e9-0310-863c-91ae7b9d1cf9
Handle ENOSYS instread of EINVAL for some helgrind tests.

Some arches (s390x and ppc64) return ENOSYS instead of EINVAL for
undefined futex operations. Adjust the helgrind filter_stderr to
handle that case.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14375 a5019735-40e9-0310-863c-91ae7b9d1cf9