emscripten: Restore compatibility with existing emsdk releases.

(cherry picked from commit 5008521538ffe7931ecd0d11c4a5e75a05f54b5b)

src/SDL_assert.c

@@ -42,7 +42,15 @@
 #endif
 
 #if defined(__EMSCRIPTEN__)
-#include <emscripten.h>
+    #include <emscripten.h>
+    /* older Emscriptens don't have this, but we need to for wasm64 compatibility. */
+    #ifndef MAIN_THREAD_EM_ASM_PTR
+        #ifdef __wasm64__
+            #error You need to upgrade your Emscripten compiler to support wasm64
+        #else
+            #define MAIN_THREAD_EM_ASM_PTR MAIN_THREAD_EM_ASM_INT
+        #endif
+    #endif
 #endif
 
 /* The size of the stack buffer to use for rendering assert messages. */
@@ -251,7 +259,7 @@ static SDL_assert_state SDLCALL SDL_PromptAssertion(const SDL_assert_data *data,
         for (;;) {
             SDL_bool okay = SDL_TRUE;
             /* *INDENT-OFF* */ /* clang-format off */
-            char *buf = (char *) EM_ASM_PTR({
+            char *buf = (char *) MAIN_THREAD_EM_ASM_PTR({
                 var str =
                     UTF8ToString($0) + '\n\n' +
                     'Abort/Retry/Ignore/AlwaysIgnore? [ariA] :';

src/video/emscripten/SDL_emscriptenmouse.c

@@ -31,6 +31,15 @@
 
 #include "../../events/SDL_mouse_c.h"
 
+/* older Emscriptens don't have this, but we need to for wasm64 compatibility. */
+#ifndef MAIN_THREAD_EM_ASM_PTR
+    #ifdef __wasm64__
+        #error You need to upgrade your Emscripten compiler to support wasm64
+    #else
+        #define MAIN_THREAD_EM_ASM_PTR MAIN_THREAD_EM_ASM_INT
+    #endif
+#endif
+
 static SDL_Cursor *Emscripten_CreateCursorFromString(const char *cursor_str, SDL_bool is_custom)
 {
     SDL_Cursor *cursor;