portability fix for MacOS X in package glib: set CXX explicitly

For some strange reason, glib's configure script initializes
CXX with "c++" instead of the cross C++ compiler. This usually
does no harm, because glib doesn't use the C++ compiler. However,
it poisons libtool's compiler lib search paths. This also usually
does no harm, except on MacOS X where it causes libtool to link
against /usr/lib/libiconv.dylib, which makes the cross build fail.

src/glib.mk

@@ -53,6 +53,7 @@ define $(PKG)_BUILD
         --with-threads=win32 \
         --with-pcre=system \
         --with-libiconv=gnu \
+        CXX='$(TARGET)-c++' \
         PKG_CONFIG='$(PREFIX)/bin/$(TARGET)-pkg-config'
     $(MAKE) -C '$(1)' -j '$(JOBS)' install bin_PROGRAMS= sbin_PROGRAMS= noinst_PROGRAMS=
 endef