recognize QT_WAYLAND_GL_CONFIG also as a qmake variable

unlike an environment variable set only for the time being, this
actually survives automated rebuilds of makefiles

diff --git a/src/qt-compositor/hardware_integration/hardware_integration.pri b/src/qt-compositor/hardware_integration/hardware_integration.pri
index 004c05f..f5a1568 100644 (file)
--- a/src/qt-compositor/hardware_integration/hardware_integration.pri
+++ b/src/qt-compositor/hardware_integration/hardware_integration.pri
@@ -1,4 +1,4 @@
-QT_WAYLAND_GL_CONFIG = $$(QT_WAYLAND_GL_CONFIG)
+isEmpty(QT_WAYLAND_GL_CONFIG):QT_WAYLAND_GL_CONFIG = $$(QT_WAYLAND_GL_CONFIG)
 
 contains(QT_CONFIG, opengl):!isEqual(QT_WAYLAND_GL_CONFIG,nogl) {
     HEADERS += \