CI: build: fix ccache cache usage

CI: build: fix ccache cache usage

CCache cache is currently broken due to a funny bug in ccache compiler
type detection. It seems ccache compiler type detection is very fragile
and with the use of external toolchain doesn't correctly detect the
type.
The type detected is set to other instead of gcc resulting in ccache
complaining for unsupported compiler options.

To handle this problem, force the compiler type to gcc to make ccache
correctly work and speedup compilation.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>