Add makefile for building with clang --target=xcore
Liberally sprinkle overlay attribute.
Improve clang makefile.
Replace magic constants with defines.
Update .gitignore
Remove l_sdl.c
Provide wrappers for various functions to i_system.h
Compare return value of strcmp against 0.
Fix detection of endianness on xCORE.
Remove unused defines.
Add XC main.
Add lcd driver.

For now this is copied from https://github.com/xcore/sw_chip8.
Fix rendering in low res mode.
Remove assembly files.
Change R_Draw(|TL)Column from a function pointer to a function.
Start to flesh out video for the xCORE.
Avoid use of SDL outside the system specific files.
Implement I_GetTime_RealTime on xCORE, some other fixes

With this change DOOM is now showing signs of life.
Rename file, no functionality change.
Add a new file for xCORE system helper functions.