crossgcc: invoke buildgcc with bash, instead of relying on #!/bin/bash

Change-Id: I09192e57e2535b2f8f98cabeb755f10c5520c499
Signed-off-by: Jonathan A. Kollasch <jakllsch@kollasch.net>
Reviewed-on: http://review.coreboot.org/151
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
Tested-by: build bot (Jenkins)

util/crossgcc/Makefile

@@ -1,11 +1,11 @@
 all: build
 
 build:
-	./buildgcc
+	bash ./buildgcc
 
 .PHONY: build-without-gdb
 build-without-gdb:
-	./buildgcc --skip-gdb
+	bash ./buildgcc --skip-gdb
 
 clean:
 	rm -rf xgcc