gfortran: update runtime dependencies

It fails to run both `gcc` and `gfortran` with errors:

| root@qemux86-64:~# x86_64-poky-linux-gcc a.c
| x86_64-poky-linux-gcc: fatal error: cannot execute 'as': posix_spawnp: No such file or directory

then add binutils which provides `as` to RDEPENDS of gcc.

libgfortran-dev provides libgfortran.spec which required by gfortran:

| root@qemux86-64:~# gfortran hello.f95
| gfortran: fatal error: cannot read spec file 'libgfortran.spec': No such file or directory

And gcc provides liblto_plugin.so:

| root@qemux86-64:~# gfortran hello.f95
| gfortran: fatal error: '-fuse-linker-plugin', but liblto_plugin.so not found

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>