Pass -flto as part of CC and CXX when building external libs for Android

Using -flto and Clang still doesn't work, though, build stops already in
fontconfig. The linker claims the expat library doesn't have an archive symbol
table. Go figure, oh well, won't bother trying any more for now.

Change-Id: Icbd65269e958665704104322e66a5b3a78fac75e

configure.ac

@@ -391,6 +391,12 @@ if test -n "$with_android_ndk"; then
         ;;
     esac
 
+    if test "$ENABLE_LTO" = TRUE; then
+        # -flto comes from com_GCC_degs.mk, too, but we need to make sure it gets passed as part of
+        # $CC and $CXX when building external libraries
+        ANDROIDCFLAGS="$ANDROIDCFLAGS -flto"
+    fi
+
     # gdbserver can be in different locations
     if test -f $ANDROID_NDK_HOME/toolchains/arm-linux-androideabi-4.4.3/prebuilt/gdbserver; then
         ANDROID_NDK_GDBSERVER=$ANDROID_NDK_HOME/toolchains/arm-linux-androideabi-4.4.3/prebuilt/gdbserver