CMakePM: Use junctions for source/build dirs on Windows

This way we have fixed small (max 64 bytes) paths for CMake's configure
/ build / install steps.

This allows the user to have longer paths and still compile with MSVC /
GCC MinGW compilers.

Fixes: QTCREATORBUG-26786
Task-number: QTBUG-117413
Change-Id: I0cff6521626dd2ce78d0223d46f0b480e977d5c5
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildstep.cpp

@@ -11,6 +11,7 @@
 #include "cmakeprojectconstants.h"
 #include "cmakeprojectmanagertr.h"
 #include "cmaketool.h"
+#include "cmaketoolmanager.h"
 
 #include <android/androidconstants.h>
 
@@ -438,7 +439,7 @@ CommandLine CMakeBuildStep::cmakeCommand() const
     if (buildConfiguration())
         buildDirectory = buildConfiguration()->buildDirectory();
 
-    cmd.addArgs({"--build", buildDirectory.path()});
+    cmd.addArgs({"--build", CMakeToolManager::mappedFilePath(buildDirectory).path()});
 
     cmd.addArg("--target");
     cmd.addArgs(Utils::transform(m_buildTargets, [this](const QString &s) {