CMakePM: Add QTC_RUN environment variable for the CMake run

This way one can do certain things knowing that CMake is being run in Qt
Creator.

Change-Id: If3ac8a52f30f9fa73a756212199a25632c757dcd
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cmakeprojectmanager/builddirparameters.cpp

@@ -65,6 +65,8 @@ BuildDirParameters::BuildDirParameters(CMakeBuildSystem *buildSystem)
     if (Utils::HostOsInfo::isAnyUnixHost())
         environment.set("ICECC", "no");
 
+    environment.set("QTC_RUN", "1");
+
     cmakeToolId = CMakeKitAspect::cmakeToolId(k);
 }