ccache: Support USE_CCACHE even in standalone build.

When USE_CCACHE is set to 1 in your environment, android-rebuild.sh
will use the 'ccache' binary in your PATH to cache compilations,
speeding up the build.

Note that this is already the case when performing a build within
the Android platform tree.

Change-Id: I04211db9e2217d4b82ed7346de7a441628adfa01
diff --git a/android-configure.sh b/android-configure.sh
index bfc8e3f..d9ca152 100755
--- a/android-configure.sh
+++ b/android-configure.sh
@@ -253,6 +253,15 @@
         fi
     fi
 else
+    if [ -n "$USE_CCACHE" ]; then
+        CCACHE=$(which ccache 2>/dev/null)
+        if [ -n "$CCACHE" -a -f "$CCACHE" ] ; then
+            CC="$CCACHE $CC"
+            log "Prebuilt   : CCACHE=$CCACHE"
+	else
+            log "Prebuilt   : CCACHE can't be found"
+        fi
+    fi
     if [ "$GLES_PROBE" = "yes" ]; then
         GLES_SUPPORT=yes
         if [ -z "$GLES_INCLUDE" ]; then