The top level Makefile.am hard codes /usr/include/linux/input.h for use 
in the generation of extras/keymap/keys.txt. Such hard coding does not 
work when cross compiling as the linux/input.h file that should be used 
is the cross environment's linux/include.h not /usr/include/linux/input.h.

I have attached a patch that determines the correct linux/include.h file 
during configure. The configure change makes use of the 
AX_ABOLUTE_HEADER 
http://www.nongnu.org/autoconf-archive/ax_absolute_header.html, which 
the patch adds to the m4.