gcc and gdb: fix fetching linaro builds (part two)

It's not my day.

linaro_version is a filter. If it is not a linaro toolchain, it will
just be CT_{CC,GDB}_VERSION. If it is a linaro toolchain, CT_{CC,GDB}_VERSION
will be prefixed with 'linaro-' and will not match linaro_version, as
linaro_version will just have the part after 'linaro-'.

This *really* fixes the issue :sigh:

Thanks again to @elsonwei for being right the first time!

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>