Change to find two XrandR header files from invidual directory.
"Xrandr.h" is in `libXrandr`, and "randr.h" is in `xorgproto` (used to be
`randrproto`) package, so they may be installed into different prefix.
Signed-off-by: OBATA Akio <obache@wizdas.com>
(cherry picked from commit bade711c82)