Wayland GLEW fix: use __linux__ and WAYLAND_DISPLAY, keep X11 errors

- #ifdef linux isn't defined under -std=c++2c/c++23, which CppMode builds with
- the env var is WAYLAND_DISPLAY (underscore)
- only NO_GLX_DISPLAY on Wayland is ignored; every other glewInit error is still reported
- drop the duplicated glewExperimental line

Author: pepc84

src/Processing.cpp

@@ -3628,13 +3628,15 @@ void PApplet::run(){
     });
     glfwMakeContextCurrent(gWindow);
     glewExperimental = GL_TRUE;
-    glewExperimental = GL_TRUE;
     GLenum glewErr = glewInit();
-#ifdef linux
-    if(glewErr != GLEW_OK && getenv("WAYLAND-DISPLAY") != nullptr && glewErr != GLEW_ERROR_NO_GLX_DISPLAY){
-#else
-    if(glewErr != GLEW_OK){
+    bool glewOk = (glewErr == GLEW_OK);
+#if defined(__linux__) && defined(GLEW_ERROR_NO_GLX_DISPLAY)
+    // A GLX-built GLEW reports NO_GLX_DISPLAY under native Wayland (GLFW uses EGL there),
+    // but the core GL functions are already loaded by then, so it's safe to carry on.
+    if (!glewOk && glewErr == GLEW_ERROR_NO_GLX_DISPLAY && getenv("WAYLAND_DISPLAY") != nullptr)
+        glewOk = true;
 #endif
+    if(!glewOk){
 
 #ifdef _WIN32
         char msg[256]; snprintf(msg,sizeof(msg),"glewInit() failed: %s", glewGetErrorString(glewErr));