tools/thermal: tmon: use pkg-config also for CFLAGS

The header <panel.h> might be in /usr/include/ncursesw, which is not
part of the standard include path. This fixes compile on openSUSE.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>