cmSystemTools: Revert GetRealPath implementation on Windows

The use of `uv_fs_realpath` introduced by commit v3.11.0-rc1~445^2~1
(cmSystemTools: Implement GetRealPath on Windows, 2017-10-02) causes
`subst` drives to be expanded on Windows, breaking existing use cases.
Revert its use until an alternative implementation can be chosen.

Preserve the behavior introduced by commit v3.11.0-rc1~445^2
(cmTimestamp: For symlinks switch to timestamp of resolved path,
2017-10-02) by retaining use of `uv_fs_realpath` in a function of
a different name.

Fixes: #18033
Issue: #17206

Help/release/3.11.rst

@@ -298,3 +298,10 @@ Changes made since CMake 3.11.0 include the following.
   :prop_sf:`SKIP_AUTOUIC` on their generated files.  These files never
   need to be processed by moc or uic, and we must say so explicitly to
   account for policy :policy:`CMP0071`.
+
+3.11.3
+------
+
+* CMake 3.11.0 introduced support for resolving symbolic links on
+  Windows in code paths that typically do so on UNIX.  This has been
+  reverted due to breakage on ``subst`` drives.

Source/cmSystemTools.cxx

@@ -949,10 +949,12 @@ cmSystemTools::WindowsFileRetry cmSystemTools::GetWindowsFileRetry()
   }
   return retry;
 }
+#endif
 
-std::string cmSystemTools::GetRealPath(const std::string& path,
+std::string cmSystemTools::GetRealPathResolvingWindowsSubst(
-                                       std::string* errorMessage)
+  const std::string& path, std::string* errorMessage)
 {
+#ifdef _WIN32
   // uv_fs_realpath uses Windows Vista API so fallback to kwsys if not found
   std::string resolved_path;
   uv_fs_t req;
@@ -981,8 +983,10 @@ std::string cmSystemTools::GetRealPath(const std::string& path,
     resolved_path = path;
   }
   return resolved_path;
-}
+#else
+  return cmsys::SystemTools::GetRealPath(path, errorMessage);
 #endif
+}
 
 void cmSystemTools::InitializeLibUV()
 {

Source/cmSystemTools.h

@@ -500,12 +500,14 @@ public:
     unsigned int Delay;
   };
   static WindowsFileRetry GetWindowsFileRetry();
-
-  /** Get the real path for a given path, removing all symlinks. */
-  static std::string GetRealPath(const std::string& path,
-                                 std::string* errorMessage = 0);
 #endif
 
+  /** Get the real path for a given path, removing all symlinks.
+      This variant of GetRealPath also works on Windows but will
+      resolve subst drives too.  */
+  static std::string GetRealPathResolvingWindowsSubst(
+    const std::string& path, std::string* errorMessage = nullptr);
+
   /** Perform one-time initialization of libuv.  */
   static void InitializeLibUV();
 

Source/cmTimestamp.cxx

@@ -33,7 +33,8 @@ std::string cmTimestamp::FileModificationTime(const char* path,
                                               const std::string& formatString,
                                               bool utcFlag)
 {
-  std::string real_path = cmSystemTools::GetRealPath(path);
+  std::string real_path =
+    cmSystemTools::GetRealPathResolvingWindowsSubst(path);
 
   if (!cmsys::SystemTools::FileExists(real_path)) {
     return std::string();