[Web] Force emcc to use "wasm" longjmp mode

SUPPORT_LONGJMP have changed since emscripten 3.1.32 to default to
"wasm" mode when exceptions are enabled, and "emscripten" mode when
disabled.

While we generally doesn't use exception in core, linked libraries may
need them, and emscripten don't plan to support WASM EH + Emscripten
SjLj in the long term.

platform/web/detect.py

@@ -276,6 +276,10 @@ def configure(env: "SConsEnvironment"):
     # Wrap the JavaScript support code around a closure named Godot.
     env.Append(LINKFLAGS=["-sMODULARIZE=1", "-sEXPORT_NAME='Godot'"])
 
+    # Force long jump mode to 'wasm'
+    env.Append(CCFLAGS=["-sSUPPORT_LONGJMP='wasm'"])
+    env.Append(LINKFLAGS=["-sSUPPORT_LONGJMP='wasm'"])
+
     # Allow increasing memory buffer size during runtime. This is efficient
     # when using WebAssembly (in comparison to asm.js) and works well for
     # us since we don't know requirements at compile-time.