Two different xmlparse libraries are created: ascii_expat_xmlparse and
expat_xmlparse. One without -DXML_UNICODE and one with. Source file are
duplicated and renamed with gb_UnpackedTarball_set_post_action function
to be able to add artifacts twice to gbuild machinery.

On windows 64 bit additional two librares are created: expat_xmlparse_x64 and
expat_xmltok_x64. That is due the problem with shell/shlxthandler (comment):
------------------------------------------------------
use UNICODE only because shell/shlxthandler
doesn't link against ascii_expat_xmlparse
------------------------------------------------------

Include files are delivered to $(OUTDIR)/inc/external/expat
now and not to $(OUTDIR)/inc/external any more.
set_include call is added in RepositoryExternal.mk.

To define dependency between StaticLibrary and ExternalProject
new function was introduced: gb_StaticLibrary_use_external_project.

Change-Id: I3b3aa40f39ef82c70f6f28790b582c83e48bdf76