General: Fix recent menuselect-related cross compile regression

MAKE_MENUSELECT currently sets CC to CC, which is the compiler for the
target platform. But menuselect is to be run on the build system, so
BUILD_CC needs to be used instead - like it was in the past, before the
recent changes (https://reviewboard.asterisk.org/r/4370/). This is the
patch for ASTERISK-25074.

ASTERISK-25074 #close
Reported by: Sebastian Kemper
Tested by: Sebastian Kemper

Change-Id: I8a2b1fc5deb6ad2b80f49baca35b1b13d468ebf8

Makefile

@@ -933,7 +933,7 @@ nmenuselect: menuselect/nmenuselect menuselect-tree menuselect.makeopts
 	-@menuselect/nmenuselect menuselect.makeopts && (echo "menuselect changes saved!"; rm -f channels/h323/Makefile.ast main/asterisk) || echo "menuselect changes NOT saved!"
 
 # options for make in menuselect/
-MAKE_MENUSELECT=CC="$(CC)" CXX="$(CXX)" LD="" AR="" RANLIB="" \
+MAKE_MENUSELECT=CC="$(BUILD_CC)" CXX="$(CXX)" LD="" AR="" RANLIB="" \
 		CFLAGS="$(BUILD_CFLAGS)" LDFLAGS="$(BUILD_LDFLAGS)" \
 		$(MAKE) -C menuselect CONFIGURE_SILENT="--silent"