package/mono: force host-mono to use internal mono bootstrap compiler

This patch forces the use of internal compiler for building mono,
for more information please refer to mono official documentation
(README.md)

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/mono/mono.mk

@@ -55,6 +55,8 @@ HOST_MONO_CONF_OPTS += \
 	--with-profile4=$(if $(BR2_PACKAGE_MONO_40),yes,no) \
 	--with-profile4_5=$(if $(BR2_PACKAGE_MONO_45),yes,no)
 
+HOST_MONO_MAKE_OPTS += EXTERNAL_MCS="$(@D)/mcs/class/lib/monolite/basic.exe"
+
 HOST_MONO_DEPENDENCIES = host-monolite host-gettext
 
 define HOST_MONO_SETUP_MONOLITE