- Only use the asm code if we're on x86_64.
- More changes to decouple asm from simd.
- Check if the -Wa,--noexecstack option works.
- Support --disable-asm configure option.
Originally created by Marc Bevand and placed in the public domain.
Enable/disabled via the same --enable-simd configure switch as
the rolling checksum optimizations.
I replaced git-set-file-times with an improved version that I wrote
recently (in python3). A new script uses it to figure out the
last-modified year for each *.[ch] file and updates its copyright.
It also puts the latest year into the latest-year.h file for the
output of --version.
