Nwchem isn't build with %optflags; it uses default flags from upstream. %optflags must be used in the package build, as stipulated in the packaging guidelines. (Also, -O3 seems used in some compilation units; this can usually safely be switched to -O2 contained in %optflags.)
This has been discussed in bug #984605 It turned out that %optflags result in unstable build (tests failing), therefore I decided to use the flags set by the Nwchem project.