__ARM_ARCH_6ZK__ is a gcc specific historical typo which may not be
defined by other compilers.
https://gcc.gnu.org/ml/gcc-patches/2015-07/msg02237.html
To avoid unexpected results when building for ARMv6KZ with clang, the
correct form of the macro (ie 6KZ) needs to be tested. The incorrect
form of the macro (ie 6ZK) still needs to be tested for compatibility
with pre-2015 versions of gcc.
Provide an ARM specific a_ctz_32 helper function for architecture
versions for which it can be implemented efficiently via the "rbit"
instruction (ie all Thumb-2 capable versions of ARM v6 and above).
Update atomic.h to provide a_ctz_l in all cases (atomic_arch.h should
now only provide a_ctz_32 and/or a_ctz_64).
The generic version of a_ctz_32 now takes advantage of a_clz_32 if
available and the generic a_ctz_64 now makes use of a_ctz_32.
Some build environments pass -march and -mtune as part of CC, therefore
update configure to check both CC and CFLAGS before making the decision
to fall back to generic -march and -mtune options for x86.
Signed-off-by: Andre McCurdy <[email protected]>
