[Fedora-packaging] Build multilib gcc RPMs for both i686 and x86_64 in just one step

Hi. I need to build gcc RPMs from source including libgcc.i686 and libstdc++.i686 I don't want to run rpmbuild or mock twice with different arch argument. One is long enough. Besides, the build directory already contains all the needed files after %build phase: ./obj-x86_64-redhat-linux/x86_64-redhat-linux/32/libstdc++-v3/src/.libs/libstdc++.so.6.0.22 ./obj-x86_64-redhat-linux/x86_64-redhat-linux/32/libgcc/32/libgcc_s.so.1 The spec file from gcc-6.1.1-2.fc24.src.rpm suggests some support for that. It has multilib_64_archs and multilib_32_arch macros, but I don't know how to use them.