...in favor of gb_LinkTarget_add_generated_exception_objects.  The former would
have needed any flags to be passed in explicitly (but no call sites did), so
e.g. StaticLibrary_graphite didn't have any debug information (when building
with --enable-debug).  I guess there is no downside to having C++ exception
support enabled in these places, and using _add_generated_cxxobjects instead was
likely an oversight in the first place (at least in the case of
external/graphite/StaticLibrary_graphite.mk, it was that way ever since
1ceb47d9 "graphite: convert to gbuild", but for
no apparent reason).

Change-Id: I9986a6c5ec30a521095dbe5315e5ca649741a790