configure: Always use old_CFLAGS and old_LIBS
configure: Always use old_CFLAGS and old_LIBS

The variables used for storing CFLAGS and LIBS before temporarily
modifying them was consistent when it comes to the name, but not
when it comes to the case.

Make sure names are completely consistent.

jardasgit/libvirt,nertpinx/libvirt,datto/libvirt,olafhering/libvirt,zippy2/libvirt,eskultety/libvirt,jfehlig/libvirt,jardasgit/libvirt,olafhering/libvirt,VenkatDatta/libvirt,datto/libvirt,olafhering/libvirt,fabianfreyer/libvirt,zippy2/libvirt,libvirt/libvirt,taget/libvirt,VenkatDatta/libvirt,datto/libvirt,crobinso/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,taget/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,datto/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,eskultety/libvirt,libvirt/libvirt,fabianfreyer/libvirt,libvirt/libvirt,zippy2/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,eskultety/libvirt,crobinso/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,olafhering/libvirt,jardasgit/libvirt,eskultety/libvirt,crobinso/libvirt,taget/libvirt,jardasgit/libvirt,jardasgit/libvirt,taget/libvirt,fabianfreyer/libvirt,libvirt/libvirt,taget/libvirt,andreabolognani/libvirt,jfehlig/libvirt,zippy2/libvirt,datto/libvirt,nertpinx/libvirt,crobinso/libvirt,nertpinx/libvirt,eskultety/libvirt