Add noX11 flag to Linux compilations

This allows users that are not using X11 to still compile the
application.

build_scripts/linux/build_linux.sh

@@ -9,7 +9,7 @@ echo $MAKE_COMMAND
 mkdir -p $BUILD_DIR
 cd $BUILD_DIR
 qmake --version
-qmake -spec $QMAKE_SPEC $PROJECT_DIR
+qmake -spec $QMAKE_SPEC $PROJECT_DIR $QMAKE_EXTRAS
 $MAKE_COMMAND
 $CLANG_TIDY
 cp -r $PROJECT_DIR/src/res $BUILD_DIR/bin/linux/AdvancedSettings/

build_scripts/linux/configure.sh

@@ -18,3 +18,6 @@ else
     CLANG_TIDY="$SCRIPT_DIR/run-clang-tidy.sh"
 fi
 
+if [[ -n $NO_X11 ]]; then
+    QMAKE_EXTRAS='CONFIG+=noX11'
+fi

build_scripts/qt/sources.pri

@@ -54,9 +54,14 @@ win32 {
 }
 
 unix:!macx {
-    SOURCES += src/tabcontrollers/keyboardinput/KeyboardInputX11.cpp
-    CONFIG += x11
-    LIBS += -lXtst
+    !noX11 {
+        SOURCES += src/tabcontrollers/keyboardinput/KeyboardInputX11.cpp
+        CONFIG += x11
+        LIBS += -lXtst
+    }
+    else {
+        SOURCES += src/tabcontrollers/keyboardinput/KeyboardInputDummy.cpp
+    }
 }
 
 macx {

docs/building_for_linux.md

@@ -143,6 +143,7 @@ The following environmental variables are relevant for building the project.
 | --------------------  | ------------- |
 | `QMAKE_SPEC`              | The [mkspec](https://forum.qt.io/topic/70970/what-is-mkspecs-used-for-how-to-configure-for-my-hardware) to compile to. Either `linux-g++` or `linux-clang`. Defaults to `linux-g++`.   |
 | `USE_TIDY`              | If set a compilation database will be created and the project linted. Can only be used with `clang`.  |
+| `NO_X11`              | If set the application will be compiled without X11 specific libraries. This disables certain things like sending keystrokes from VR.  |
 
 If an environment variable isn't set a default value will be provided. The default values are shown in the table below.