ACK, but:
+MINGW_CFLAGS="%{_mingw32_cflags} -I%{_mingw32_includedir}" %{_mingw32_configure}
FPC wanted us to use mingw32/MINGW32 everywhere, so this is in fact a mistake in the base mingw32-filesystem package. That environment variable should have been called MINGW32_CFLAGS.
Rich.