BaseTools: Fix incremental build bug

BaseTools: Fix incremental build bug

https://bugzilla.tianocore.org/show_bug.cgi?id=2078

This is a build tool regression issue that
is introduced by multiple-process-autogen.

The workspace timestamp value is not pass
to module autogen object correctly, so build tool
does not detect the change of .dsc and ignore the autogen.

This patch is to fix this issue.

Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Tested-by: Michael D Kinney <michael.d.kinney@intel.com>