Pass variables to mingw-w64's configure as parameters instead of inherited via the environment

This makes sure they are remembered if automatically reconfiguring
e.g. due to updated autotools source files.

build-mingw-w64.sh

@@ -56,8 +56,8 @@ for arch in $ARCHS; do
         ;;
     esac
     FLAGS="$FLAGS --with-default-msvcrt=ucrtbase"
-    CC=$arch-w64-mingw32-clang AR=llvm-ar RANLIB=llvm-ranlib DLLTOOL=llvm-dlltool \
-    ../configure --host=$arch-w64-mingw32 --prefix=$PREFIX/$arch-w64-mingw32 $FLAGS
+    ../configure --host=$arch-w64-mingw32 --prefix=$PREFIX/$arch-w64-mingw32 $FLAGS \
+        CC=$arch-w64-mingw32-clang AR=llvm-ar RANLIB=llvm-ranlib DLLTOOL=llvm-dlltool
     make -j$CORES
     make install
     cd ..