libinput: fix missing static_assert
uClibc-ng does not define the C11 static_assert macro. Patch configure.ac to
detect this and define a nop macro.
Fixes:
http://autobuild.buildroot.net/results/3eb/
3eb32c19f90a5fd8d45a0c36676e015e8278a469/
http://autobuild.buildroot.net/results/184/
1844890c65615f1676a85c6fac78937249eee9f1/
http://autobuild.buildroot.net/results/3a3/
3a3f8c5624e8019a6eababbf6e7440fdd668f85f/
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>