contrib/libressl: use HOSTVARS, HOSTCONF with MinGW

Change-Id: I4a2d2d9a5d067569f7a3a2fafe9c5444abae0088
Reviewed-by: Sebastien Blin <sebastien.blin@savoirfairelinux.com>

contrib/src/libressl/rules.mak

@@ -48,9 +48,9 @@ libressl: portable-$(LIBRESSL_VERSION).tar.gz openbsd-$(OPENBSD_VERSION).tar.gz
 	mkdir -p "$(PREFIX)/include"
 	cd $< && ./autogen.sh
 ifdef HAVE_WIN32
-	cd $< && CC=i686-w64-mingw32-gcc CPPFLAGS=-D__MINGW_USE_VC2005_COMPAT ./configure --host=i686-w64-mingw32 && $(MAKE) && DESTDIR=$(PREFIX) $(MAKE) install
+	cd $< && $(HOSTVARS) CPPFLAGS=-D__MINGW_USE_VC2005_COMPAT ./configure $(HOSTCONF) && $(MAKE) && $(MAKE) install
 else ifdef HAVE_WIN64
-	cd $< && CC=x86_64-w64-mingw32-gcc ./configure --host=x86_64-w64-mingw32 && $(MAKE) && DESTDIR=$(PREFIX) $(MAKE) install
+	cd $< && $(HOSTVARS) ./configure $(HOSTCONF) && $(MAKE) && $(MAKE) install
 else ifeq ($(IOS_TARGET_PLATFORM),iPhoneOS)
 	cd $< && mkdir build && cd build && $(CMAKE) -DDESTDIR=$(PREFIX) -DCMAKE_C_FLAGS='-miphoneos-version-min=9.3 -fembed-bitcode -arch arm64' .. && $(MAKE) && $(MAKE) install
 else ifeq ($(IOS_TARGET_PLATFORM),iPhoneSimulator)