The following error occurs when building dtc module:

        CHK version_gen.h
         CC libfdt/fdt.o
cc1: error: dtc: No such file or directory [-Werror]
cc1: all warnings being treated as errors
make[1]: *** [libfdt/fdt.o] Error 1
make: *** [subdir-dtc] Error 2

In rules.mak, "-I$(<D) -I$(@D)" was expanded to "-Idtc -I." when
building submodule dct. Due to the using of "-Wmissing-include-dirs,
a warning would be rarsed. To avoid it, add "-I$(<D) -I$(@D)" to
QEMU_INCLUDES instead of QEMU_CFLAGS so that QEMU_CFLAGS does not
contain the "-Idtc".

Cc: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: Blue Swirl <blauwirbel@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1367247132-19622-1-git-send-email-riegamaths@gmail.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>