util/xcompile: fix XGCCPATH handling

This patch fixes the build with an external (coreboot) toolchain. When
the toolchain is not under util/crossgcc/xgcc, setting XGCCPATH to
/path/to/toolchain results in the error:

  toolchain.inc:169: The coreboot toolchain version of iasl '<date>' was
  not found

The reason is that the xcompile script incorrectly assumes XGCCPATH to
have a trailing slash.

Change-Id: Ifcc4bd2b081fa3603420dc0a8cab3b47967ebc65
Signed-off-by: Michele Guerini Rocco <rnhmjoj@inventati.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48937
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

util/xcompile/xcompile

@@ -51,7 +51,7 @@ program_exists() {
 
 
 if [ "$("${XGCCPATH}/iasl" 2>/dev/null | grep -c ACPI)" -gt 0 ]; then
-	IASL=${XGCCPATH}iasl
+	IASL=${XGCCPATH}/iasl
 elif [ "$(iasl 2>/dev/null | grep -c ACPI)" -gt 0 ]; then
 	IASL=iasl
 fi