build-mingw-w64: Fix installing COPYING files on macOS

The install(1) tool on macOS doesn't support the -D option for
creating directories at the same time while installing files.
Therefore, run a separate step for creating directories. Doing that
with "mkdir -p", even if install(1) also could do that with the -d
option (likewise with a separate command).

Also stop specifying the destination file name, when it's equal to
the source files, now that we know that the destination directory
already exists.

build-mingw-w64-tools.sh

@@ -92,7 +92,8 @@ cd build${CROSS_NAME}
 ../configure --prefix="$PREFIX" $CONFIGFLAGS
 $MAKE -j$CORES
 $MAKE install-strip
-install -Dm644 ../COPYING "$PREFIX/share/gendef/COPYING"
+mkdir -p "$PREFIX/share/gendef"
+install -m644 ../COPYING "$PREFIX/share/gendef"
 cd ../../widl
 [ -z "$CLEAN" ] || rm -rf build${CROSS_NAME}
 mkdir -p build${CROSS_NAME}
@@ -100,7 +101,8 @@ cd build${CROSS_NAME}
 ../configure --prefix="$PREFIX" --target=$ANY_ARCH-w64-mingw32 --with-widl-includedir="$INCLUDEDIR" $CONFIGFLAGS
 $MAKE -j$CORES
 $MAKE install-strip
-install -Dm644 ../../../COPYING "$PREFIX/share/widl/COPYING"
+mkdir -p "$PREFIX/share/widl"
+install -m644 ../../../COPYING "$PREFIX/share/widl"
 cd ..
 cd "$PREFIX/bin"
 # The build above produced $ANY_ARCH-w64-mingw32-widl, add symlinks to it