Clean up some ARMv4/ARMv5 cruft.

Change-Id: I29e836fea4b53901e29f96c6888869c35f6726be
Clean up the pthread-only atomic stuff a little.

It looks like we can probably just use the generic GCC stuff instead;
the generated code looks pretty similar. We should come back to that.

These routines are only used by the pthread implementation, and
__bionic_atomic_inc isn't used, so we can remove it.

Conflicts:
	libc/private/bionic_atomic_arm.h

Change-Id: I8b5b8cb30a1b159f0e85c3675aee06ddef39b429
ARM: Change dmb domain for bionic_atomic_barrier()

This patch changes the domain that the memory barrier operates on. Assumes
that the scope of bionic_atomic_barrier() does not include device memory,
memory shared with the GPU or any other memory external to the processor
cluster.

Signed-off-by: Serban Constantinescu <serban.constantinescu@arm.com>

Conflicts:
	libc/private/bionic_atomic_arm.h
	libc/private/bionic_atomic_gcc_builtin.h

Change-Id: I291e741c98a64c86f3a3cf99811bbf1e714ac9aa
Remove harmful attempts to be helpful in pthread_mutex functions.

Most callers won't check for EINVAL, so it's best to fail early.
GCC takes the nonnull attribute as a guarantee that an argument
won't be NULL, so these hacks were already ineffective, which is
how we found that at least one commercial game was using NULL
as if it's a mutex, but actually getting no-op behavior.

Bug: 11971278
Change-Id: I89646e043d931778805a8b692e07a34d076ee6bf