crossgcc: Support /bin/sh pointing to dash

It doesn't know "source", but wants the older "." instead

Change-Id: Iafa61b1d2ffc9c737ab67a417c62417593b69374
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/10974
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/util/crossgcc/buildgcc b/util/crossgcc/buildgcc
index f59b225..590e1f8 100755
--- a/util/crossgcc/buildgcc
+++ b/util/crossgcc/buildgcc
@@ -109,7 +109,7 @@
 
 please_install()
 {
-	test -r /etc/os-release && source /etc/os-release
+	test -r /etc/os-release && . /etc/os-release
 	case "$ID_LIKE" in
 	debian) solution="sudo apt-get install $1" ;;
 	suse) solution="sudo zypper install $1" ;;