Only create OpenGL context on Linux

.. MacOS Qt crashes when destroying it, OpenGL is *that*
   broken by Apple.

.. applied to Windows too, despite it not being an issue
   reported there is no value in doing it so removed.

[publish binaries]

src/Gui/GcCrashDialog.cpp

@@ -257,7 +257,9 @@ QString GcCrashDialog::versionHTML()
             "<br>DB Schema: %5"
             "<br>Metrics: %7"
             "<br>OS: %6"
+#ifdef Q_OS_LINUX
             "<br>OpenGL: %8"
+#endif
             "<br>")
             .arg(__DATE__)
             .arg(__TIME__)
@@ -270,7 +272,10 @@ QString GcCrashDialog::versionHTML()
             .arg(schemaVersion)
             .arg(os)
             .arg(factory.metricCount())
-            .arg(gl_version);
+#ifdef Q_OS_LINUX
+            .arg(gl_version)
+#endif
+            ;
 
     QString lib_version = tr(
             "<table>"

src/Gui/MainWindow.cpp

@@ -372,8 +372,9 @@ MainWindow::MainWindow(const QDir &home)
     spacer->setFixedWidth(5 *dpiYFactor);
     head->addWidget(spacer);
 
-
+#ifdef Q_OS_LINUX
     // check opengl is available with version 2 or higher
+    // only do this on Linux since Windows and MacOS have opengl "issues"
     QOffscreenSurface surf;
     surf.create();
 
@@ -384,6 +385,7 @@ MainWindow::MainWindow(const QDir &home)
     // OpenGL version number
     gl_version = QString::fromUtf8((char *)(ctx.functions()->glGetString(GL_VERSION)));
     gl_major = Utils::number(gl_version);
+#endif
 
     /*----------------------------------------------------------------------
      * Central Widget