This allows to 'mount' the SDL source directory on http://localhost:8080/SDL.
This is useful for debugging emscripten applications in the browser.
Build SDL with "-gsource-map -ffile-prefix-map=/path/to/SDL:/SDL" to
configure the URL where the source code must be available.
The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().
Anonymous Maarten