devtools: allow non-standard toolchain in meson test

devtools: allow non-standard toolchain in meson test

If a compiler is not found in $PATH, the compilation test is skipped.
In some cases, the compiler could be found after extending $PATH
in an environment configuration script (called by load-devel-config).

The decision to skip is deferred to a later stage, after loading the
configuration script.

In such case, the variable DPDK_TARGET, used by the configuration script
as input, is the compiler name.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: David Christensen <drc@linux.vnet.ibm.com>