SDL_TTF and freetype not building with PTHREADS

[cm226]

If using SDL2 with threads then sdl2_ttf.py and freetype.py don't compile a -mt version of the library automatically like sdl2.py does.

We found that the linker dosnt seem to complain about linking the non-mt versionf of these librarys, but when using TTF_OpenFont you get heap corruption at runtime.

I changed sdl2.ttf.py and freetype to compile with USE_PTHREADS, linked with those library's and it fixed the heap corruption.

[debevv]

I can confirm the issue, too
Building with the following flags:

-O3 -pthread -s USE_PTHREADS=1 -s WASM=1 -s PTHREAD_POOL_SIZE=navigator.hardwareConcurrency -s PROXY_TO_PTHREAD -s USE_SDL=2 -s USE_SDL_TTF=2 -s TOTAL_MEMORY=1024MB

produces this error:

wasm-ld: error: --shared-memory is disallowed by sfnt.c.o because it was not compiled with 'atomics' or 'bulk-memory' features.

The solution, as @cm226 advised, is to edit both tools/ports/sdl_ttf2.py and tools/ports/freetype.py by adding the -pthread flag to the build commands (then rebuilding them after emcc --clear-ports)

[kripken]

A PR to fix this would be great. See tools/ports/sdl2.py for how to handle pthreads in a port.