system/unzip: miscellaneous fixes

* Make sure CFLAGS are respected by setting LOCAL_UNZIP instead of
  LOCAL_ZIP and unsetting CFLAGS_OPT in the configure script.
* Don't strip too early by setting STRIP to a no-op and unsetting
  LFLAGS2 in the configure script.
* Cherry-pick a patch from Fedora to fix format warnings.
* Fix unzipsfx test on 32-bit arches by casting a literal argument to
  the correct type.