Ninja: disable work around when linking with mingw

The work around is only needed by older GCCs (only testet 4.4/4.7)
Ninja is very new so chances are high that there is also a new mingw.

Use slashes in link rsp file, because ar.exe can't handle \.

Modules/Platform/Windows-GNU.cmake

@@ -115,7 +115,9 @@ macro(__windows_compiler_gnu lang)
   list(APPEND CMAKE_${lang}_ABI_FILES "Platform/Windows-GNU-${lang}-ABI")
 
   # Support very long lists of object files.
-  if("${CMAKE_${lang}_RESPONSE_FILE_LINK_FLAG}" STREQUAL "@")
+  # TODO: check for which gcc versions this is still needed, not needed for gcc >= 4.4.
+  # Ninja generator doesn't support this work around.
+  if("${CMAKE_${lang}_RESPONSE_FILE_LINK_FLAG}" STREQUAL "@" AND NOT CMAKE_GENERATOR MATCHES "Ninja")
     foreach(rule CREATE_SHARED_MODULE CREATE_SHARED_LIBRARY LINK_EXECUTABLE)
       # The gcc/collect2/ld toolchain does not use response files
       # internally so we cannot pass long object lists.  Instead pass

Source/cmNinjaNormalTargetGenerator.cxx

@@ -18,6 +18,7 @@
 #include "cmMakefile.h"
 
 #include <assert.h>
+#include <algorithm>
 
 cmNinjaNormalTargetGenerator::
 cmNinjaNormalTargetGenerator(cmTarget* target)
@@ -367,8 +368,8 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
   outputs.push_back(targetOutputReal);
 
   // Compute specific libraries to link with.
-  cmNinjaDeps explicitDeps = this->GetObjects(),
-              implicitDeps = this->ComputeLinkDeps();
+  cmNinjaDeps explicitDeps = this->GetObjects();
+  cmNinjaDeps implicitDeps = this->ComputeLinkDeps();
 
   this->GetLocalGenerator()->GetTargetFlags(vars["LINK_LIBRARIES"],
                                             vars["FLAGS"],
@@ -434,6 +435,9 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
     path = GetTarget()->GetSupportDirectory();
     vars["OBJECT_DIR"] = ConvertToNinjaPath(path.c_str());
     EnsureDirectoryExists(path);
+    // ar.exe can't handle backslashes in rsp files (implictly used by gcc)
+    std::string& linkLibraries = vars["LINK_LIBRARIES"];
+    std::replace(linkLibraries.begin(), linkLibraries.end(), '\\', '/');
     }
 
   std::vector<cmCustomCommand> *cmdLists[3] = {