Disable std univ in spec for el5

A change introduced in 7.9.7 (c2f6034b) breaks the glibc external
build in el5 for some reason... Seems to have to do with the distinction
between 'export CFLAGS=...; make xyz' vs 'make CFLAGS=... xyz', and also
involves the CFLAGS that the %cmake macro would otherwise export.

In any case, std univ won't build for el5 until this gets fixed...
Hack up makesrpm script to work with el5

Unfortunately rpm/rpmbuild in el5 seems to put -D macros last in
priority, so there's not way to override the %_topdir set in a
~/.rpmmacros file except for adding another macros file...
Use %undefined macro in spec