Disable LLVM's use of __DATE__ and __TIME__ macros.

Disable LLVM's use of __DATE__ and __TIME__ macros.

Timestamp macros make the build unreproducible. This is of particular concern
to Android, but since LLVM only uses them for command line operations which
we don't need at all, they can be disabled on all platforms.

Bug 27079084

Change-Id: I2c4c3dcd06feb3a64936e70ca1535f5a12816e95
Reviewed-on: https://swiftshader-review.googlesource.com/4730
Reviewed-by: Keun Soo Yim <yim@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>