gbuild: SdiTarget: .hxx file is always out-of-date

... so touch it to avoid that, just to avoid the "true" rule from being
invoked every time.

Change-Id: I6f27c6e4b0d071b9877a38dc1f4cd3c3eb10bfc0
gbuild: AllLangResTarget: avoid spurious rebuilds on missing translation

... if the darn files are allowed to be missing, use wildcard to avoid
dependencies on them.

Change-Id: I5232efcb17342d0b2a1e909da6449b08c4148245
gbuild: HelpTarget: avoid spurious rebuilds on missing translation

... if the darn files are allowed to be missing, use wildcard to avoid
dependencies on them.

Change-Id: I36a83413f8fb65b081681a8f351ec6afcf15fe6d
gbuild: Extension: avoid re-build on missing translation description.xml

Change-Id: I6292f4ec235f8880176c2671ec7c8533168cdbeb