A project being built entirely statically will call pkg-config with
--static, which utilises the Libs.private field. Conversely it will
not use --static when not being built entirely statically, even if
there is only a static build of SDL available. This will most likely
cause the build to fail due to underlinking unless we merge the Libs
fields.
This is what the Meson build system does when it generates pkg-config
files. This also also follows the behaviour of sdl2-config.
At the same time, the runtime linker flags are not applicable to
static-only builds so only add them for shared builds.
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().
