util/crossgcc: derive date and version from latest commit

This way date and version are automatically updated when util/crossgcc
was changed, the version contains the commit ID and we have less churn
on these variables.

Change-Id: I475ba9578a8bb421d7c342d2569d7de7fcf4161d
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/30804
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

util/crossgcc/buildgcc

@@ -30,8 +30,8 @@
 
 cd "$(dirname "$0")" || exit 1
 
-CROSSGCC_DATE="January 9th, 2019"
-CROSSGCC_VERSION="1.56"
+CROSSGCC_DATE="$(git log -n 1 --pretty=%ad --date=short .)"
+CROSSGCC_VERSION="$(git describe $(git log -n 1 --pretty=%h .))"
 CROSSGCC_COMMIT=$( git describe )
 
 # default settings