build system: Only test for git once

And then use the variable to decide what to do.

Change-Id: I48a801ecdbf774c4a8b64d7efaf9cf0ef2c2d438
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/8600
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed