Change CFLAGS handling for glibc external in el5

In 7.9.7 (c2f6034b), a bunch of similar cmake lines were changed from
"make CFLAGS=..." to "export CFLAGS=... make", which actually behave
differently, and in el5 this change breaks the glibc build in the rpm
rpm builds, which set CFLAGS in the environment before running cmake...
Build std univ for el5 again, with glibc fix