This will help us deal with shader name collision. Breaks the Windows
build for the moment, unfortunately.

All these changes will allow us to more easily add Lol Engine as a
submodule of another Git project.

If SDL_CFLAGS is defined to a non-empty value, even spaces, a later
test will wrongly succeed and think SDL_CFLAGS is a user override.

no known regressions yet.

an apk for each project.

compiler bugs in the Xcode toolchain.

crashing from an assertion failure.

flags that autoconf hasn’t checked first.

disabled until the engine code itself is ported to SDL2.

to external so as to avoid some autocompletion collisions with "configure".

that the OpenGL framework on OS X provides GL version 2 at least.

when building for the PS3 on a Unix system.

it understands V=0 and V=1.

accept them as variable names.