test/run_device_tests.py: Allow specifying compiler
test/run_device_tests.py: Allow specifying compiler

Default to using gcc, but allow selecting clang so that we can test it.

BRANCH=none
BUG=b:172020503
TEST=./test/run_device_tests.py --compiler clang --board dartmonkey
       --tests sha256 --remote 127.0.0.1:2551
TEST=./test/run_device_tests.py --board dartmonkey
       --tests sha256 --remote 127.0.0.1:2551

Signed-off-by: Tom Hughes <fc5c12f30a5ed2baa0581f44ee14ad1eb7b20d83@chromium.org>
Change-Id: I3cfd04825df8cac54fbee1ba1b084ea581e62e53
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3172037
Reviewed-by: Craig Hesling <383db090fd8ef907a606ac8a9eccd2962bc489cf@chromium.org>
Reviewed-by: Patryk Duda <213d388d1c6ea6afd34b87da9fc4415c3231b04c@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec