Move the check for SOURCE_DATE_EPOCH to the driver and use a cc1 option
to pass it to the frontend. This avoids hidden state in the cc1
invocation and makes this env variable behave more like other env
variables that clang handles in the driver.
Differential Revision: https://reviews.llvm.org/D136717
See https://reproducible-builds.org/docs/source-date-epoch/ . The environment
variable ``SOURCE_DATE_EPOCH`` been recognized by many compilers.
In GCC, if `SOURCE_DATE_EPOCH` is set, it specifies a UNIX timestamp to be used
in replacement of the current date and time in the `__DATE__` and `__TIME__`
macros. Note: GCC as of today does not update `__TIMESTAMP__` (the modification
time of the current source file) but
https://wiki.debian.org/ReproducibleBuilds/TimestampsFromCPPMacros expresses the
intention to update it.
This patches parses SOURCE_DATE_EPOCH and changes all the three macros.
In addition, in case gmtime/localtime returns null (e.g. on 64-bit Windows
gmtime returns null when the timestamp is larger than 32536850399
(3001-01-19T21:59:59Z)), use `??? ?? ????` as used by GCC.
Reviewed By: ychen
Differential Revision: https://reviews.llvm.org/D135045
