devtools: test compiler availability only once

devtools: test compiler availability only once

The compilation test is skipped if the compiler is not available.
In the case of gcc/arm, it was tested both in the generic function
"build" and in the cross-compilation section.

By passing the compiler as argument of the generic function,
the test with "command" is done only once.

This small clean-up has the benefit of introducing the compiler
parameter to be used later in another improvement.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Luca Boccassi <bluca@debian.org>