Use a dummy icu-config when cross-compiling harfbuzz (to Android)

Seems that when cross-compiling to Android from Linux, we apparently
have used either the build platform's pkg-config files for ICU, or the
build platform's icu-config. Both of which are obviously the wrong
thing to do, but apparently it has worked by accident anyway.

This makes building for Android on OS X proceed past harfbuzz, at least.

Change-Id: I27351f6177438697a1cded642c8c669ba7221009

external/harfbuzz/ExternalProject_harfbuzz.mk

@@ -21,6 +21,7 @@ $(eval $(call gb_ExternalProject_use_externals,harfbuzz,\
 
 $(call gb_ExternalProject_get_state_target,harfbuzz,build) :
 	$(call gb_ExternalProject_run,build,\
+		$(if $(CROSS_COMPILING),PATH=$(SRCDIR)/external/icu/cross-bin:$$PATH) \
 		./configure \
 			--enable-static \
 			--disable-shared \

external/icu/cross-bin/icu-config

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+case $1 in
+--version)
+    echo whatever
+    ;;
+--cppflags)
+    echo ${ICU_CFLAGS}
+    ;;
+--ldflags-searchpath)
+    echo ${ICU_LIBS}
+esac