* On Mac, nss-config must not emit -rpath-link switch.
* --with-system-nss/-nspr horribly broke in combination with the
  routine use of MOZ_ARCH and resulting MOZ_CROSS_COMPILE for Mac,
  and the latter appears to be unnecessary for a normal build, anyway,
  so is now conditional CREATE_UNIVERSAL_MAC_MOZ_ZIP, in case anybody
  still uses the code to create universal moz archives.
* This in turn revealed two issues in moz that have been addressed
  with a new macosx_build_fix.patch.