In the spec file of zip-2.3-4, the %build section is:
> make -f unix/Makefile prefix=/usr "RPM_OPT_FLAGS=$RPM_OPT_FLAGS"
generic_gcc

The definition of RPM_OPT_FLAGS is of absolutely no use, as that string is
totally unknown in the package (and the patch).

I suggest using $LOCAL_ZIP ($(LOCAL_ZIP) in the unix/Makefile), as it is
otherwise unused, and as redefining CFLAGS conflicts with some other flags
(-I. -DUNIX would have to be added). Unless of course, the "-O2" of the
original CFLAGS aren't overridden by the RPM_OPT_FLAGS, which I
unfortunately couldn't read out of the gcc documentation.

> make -f unix/Makefile prefix=/usr LOCAL_ZIP="$RPM_OPT_FLAGS" generic_gcc
or
> make -f unix/Makefile prefix=/usr CFLAGS="$RPM_OPT_FLAGS -I. -DUNIX"
generic_gcc

While you're at it, make "prefix=/usr" to "prefix=%{prefix}" (and replace
it in all the other places) - it _is_ defined in the spec file's header
already.