build: Propagate CFLAGS to g-ir-scanner
build: Propagate CFLAGS to g-ir-scanner

I'm trying to build rpm-ostree with `-fsanitize=address`, and
the libdnf introspection build bombs out because it doesn't include
`-fsanitize` in the scanner build.

`Makefile.introspection` does this for us, but since we're using
CMake we need to propagate manually.

Closes: #227
Approved by: Conan-Kudo

rpm-software-management/libhif,hughsie/libhif,rpm-software-management/libhif,hughsie/libhif,Conan-Kudo/libhif,hughsie/libhif,Conan-Kudo/libhif,edynox/libdnf,rpm-software-management/libdnf,rpm-software-management/libdnf,edynox/libdnf,edynox/libdnf,rpm-software-management/libhif,Conan-Kudo/libhif,Conan-Kudo/libhif,rpm-software-management/libdnf,edynox/libdnf,hughsie/libhif,rpm-software-management/libhif,rpm-software-management/libdnf