Android update and small improvements

-fixed code do cross compiling to android
-fixed build with GCC (workaround)
-added little benchmark
-several small fixes
-updated meson build (demos building, working with GCC, LDC and DMD)
-added some meson options
-added ImGUI bind for OpenGL3

demos/external/wasm_imports/bindbc/sdl/dynload.d

@@ -14,8 +14,8 @@ import bindbc.sdl.config,
        bindbc.sdl.bind;
 
 private {
-    SharedLib lib;
-    SDLSupport loadedVersion;
+    __gshared SharedLib lib;
+    __gshared SDLSupport loadedVersion;
 }
 
 void unloadSDL()
@@ -664,14 +664,14 @@ SDLSupport loadSDL(const(char)* libName)
         lib.bindSymbol(cast(void**)&SDL_HasColorKey, "SDL_HasColorKey");
         lib.bindSymbol(cast(void**)&SDL_GetDisplayOrientation, "SDL_GetDisplayOrientation");
 
-        version(linux) {
-            lib.bindSymbol(cast(void**)&SDL_LinuxSetThreadPriority, "SDL_LinuxSetThreadPriority");
-        }
-        else version(Android) {
+        version(Android) {
             lib.bindSymbol(cast(void**)&SDL_IsChromebook, "SDL_IsChromebook");
             lib.bindSymbol(cast(void**)&SDL_IsDeXMode, "SDL_IsDeXMode");
             lib.bindSymbol(cast(void**)&SDL_AndroidBackButton, "SDL_AndroidBackButton");
         }
+        else version(linux) {
+            lib.bindSymbol(cast(void**)&SDL_LinuxSetThreadPriority, "SDL_LinuxSetThreadPriority");
+        }
 
         if(errorCount() != errCount) return SDLSupport.badLibrary;
         else loadedVersion = SDLSupport.sdl209;

demos/external/wasm_imports/bindbc/sdl/image.d

@@ -229,8 +229,8 @@ else {
     }
 
     private {
-        SharedLib lib;
-        SDLImageSupport loadedVersion;
+        __gshared SharedLib lib;
+        __gshared SDLImageSupport loadedVersion;
     }
 
     void unloadSDLImage()