buildroot

lua-sdl2: fix build without C++ compiler

lua-sdl2 CMakeLists.txt files did not explicitly indicate that it's a
C-only project, and therefore CMake by default tries to find a C++
compiler, causing a build failure when none was available.

This commit fixes that by adding a patch that adjusts the project()
definitions in CMakeLists.txt.

Fixes:

  http://autobuild.buildroot.net/results/45e39562a68c236c582861d410ee1a9924f2bfc5/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>