If SOURCE_DATE_EPOCH is set, `touch` all source files between the (optional)
prepare() and build() functions to unify the modification times. This works
around build systems and compilers that embed the file modification times
into the file contents of release artifacts.
Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>