build: Check if arch is VAX or compiler is MSVC.
* configure.ac (AH_BOTTOM): Add check for VAX and MSVC. * src/const-time.h (POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON): Rename.
Cherry-pick master commit of:
c848459e512615c1865a23cf24debb3ad4a1e85b
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>