Makefile.shared sets ONLY_ACTIVE_ARCH=NO whenever ARCHS is set, and Plugin.32 cannot build when ARCHS=x86_64. This is different from what happens for "set-wevbkit-configuration --64-bit; make". In the latter case, the makefile doesn't do special custom for architectures (unless OVERRIDE_ARCHS is set, which is only done in LayoutTestRelay/Makefile). So ONLY_ACTIVE_ARCH remains at YES, and xcconfig files do their magic to override VALID_ARCHS and have Plugin.32 build as 64-bit.
Created attachment 283885 [details] proposed fix
Comment on attachment 283885 [details] proposed fix Clearing flags on attachment: 283885 Committed r203348: <http://trac.webkit.org/changeset/203348>
All reviewed patches have been landed. Closing bug.