Build breaks with MAGNUM_WITH_TRIANGLE_SOKOL_EXAMPLE=ON: use of undeclared identifier 'flextInit'

[yurivict]

/usr/ports/graphics/magnum-examples/work/magnum-examples-2020.06-265-gb843f07a/src/triangle-sokol/TriangleSokolExample.cpp:80:5: error: use of undeclared identifier 'flextInit'
   80 |     flextInit();
      |     ^
1 error generated.

clang-18
FreeBSD 14.1

[mosra]

Yeah, I'm aware of this. Unfortunately this example only works when Magnum is built w/o MAGNUM_TARGET_GL, as otherwise the GL symbols from Magnum and from the example itself, used by sokol_gfx, clash with each other. So, the "solution" is to not build this example at all.

I'll add a better error message for this.