$ emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.8-git (70404efec4458b60b9
53bc8f1529f2fa112cdfd1)
clang version 21.0.0git
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: C:/msys64/clang64/opt/emscripten-llvm/bin

$ pkgconf --list-all | grep -i SDL | sort | uniq
SDL2_gfx                       SDL2_gfx - drawing and graphical effects extension for SDL
SDL2_image                     SDL2_image - image loading library for Simple DirectMedia Layer
SDL2_net                       SDL2_net - net library for Simple DirectMedia Layer
SDL2_ttf                       SDL2_ttf - ttf library for Simple DirectMedia Layer with FreeType 2 support
sdl2                           sdl2 - Simple DirectMedia Layer is a cross-platform multimedia library designed to provide low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D video framebuffer.

$ emmake pkgconf --list-all
make: pkgconf --list-all
egl                            egl - EGL library
glesv2                         glesv2 - OpenGL ES 2.0 library
glfw3                          GLFW - A multi-platform library for OpenGL, window and input
sdl                            sdl - Simple DirectMedia Layer is a cross-platform multimedia library designed to provide low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D video framebuffer.

$ emcc --show-ports | grep SDL
    sdl2 (-sUSE_SDL=2 or --use-port=sdl2; zlib license)
    sdl2_gfx (-sUSE_SDL_GFX=2 or --use-port=sdl2_gfx; zlib license)
    sdl2_image (-sUSE_SDL_IMAGE=2 or --use-port=sdl2_image; zlib license)
    sdl2_mixer (-sUSE_SDL_MIXER=2 or --use-port=sdl2_mixer; zlib license)
    sdl2_net (-sUSE_SDL_NET=2 or --use-port=sdl2_net; zlib license)
    sdl2_ttf (-sUSE_SDL_TTF=2 or --use-port=sdl2_ttf; zlib license)
    sdl2 (-sUSE_SDL=3 or --use-port=sdl3; zlib license)

$ emmake pkgconf --cflags sdl # I suppose this is the SDL 1.x port, not 2.x
make: pkgconf --cflags sdl
-D_GNU_SOURCE=1 -D_REENTRANT

$ pkgconf --cflags SDL2
-IC:/msys64/clang64/include/SDL2 -Dmain=SDL_main
$ pkgconf --libs SDL2
-lmingw32 -mwindows -lSDL2main -lSDL2