build_cross_tools: Have scripts exit on failure.

Previously they just silently continued, which meant that if part of the
cross-tools build failed, you would have to scroll back pretty far to
see what the failure was.

build/scripts/build_cross_tools

@@ -11,6 +11,8 @@ if [ $# -lt 3 ]; then
 	exit 1
 fi
 
+set -e
+
 haikuSourceDir=$1
 buildToolsDir=$2/legacy
 installDir=$3

build/scripts/build_cross_tools_gcc4

@@ -9,6 +9,8 @@ if [ $# -lt 4 ]; then
 	exit 1
 fi
 
+set -e
+
 haikuMachine=$1
 haikuSourceDir=$2
 buildToolsDir=$3