This patch fixes build when any of the include paths from QEMU_CFLAGS
contains a header file with similar name to a header file in qemu
sources. I hit it with error.h included by qapi/qapi-types-core.h. GCC
decided to use /usr/include/alsa/error.h instead of qemu's error.h.

Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>