Use forward slashes for objects in response files

Response files are parsed by tools, not by shells.  We teach
cmLocalGenerator::Convert() a new "RESPONSE" output format and use it
for objects listed in response files.  It does not do special slash or
MSYS root translation like the "SHELL" format does.  This is necessary
for GNU tools on Windows to understand response file content.

See issue #10401.

Source/cmLocalGenerator.cxx

@@ -2247,6 +2247,10 @@ std::string cmLocalGenerator::ConvertToOutputFormat(const char* source,
       }
     result = this->EscapeForShell(result.c_str(), true, false);
     }
+  else if(output == RESPONSE)
+    {
+    result = this->EscapeForShell(result.c_str(), false, false);
+    }
   return result;
 }
 

Source/cmLocalGenerator.h

@@ -102,7 +102,7 @@ public:
    * path setting
    */
   enum RelativeRoot { NONE, FULL, HOME, START, HOME_OUTPUT, START_OUTPUT };
-  enum OutputFormat { UNCHANGED, MAKEFILE, SHELL };
+  enum OutputFormat { UNCHANGED, MAKEFILE, SHELL, RESPONSE };
   std::string ConvertToOutputFormat(const char* source, OutputFormat output);
   std::string Convert(const char* remote, RelativeRoot local,
                       OutputFormat output = UNCHANGED,

Source/cmMakefileTargetGenerator.cxx

@@ -1329,7 +1329,7 @@ public:
     this->NextObject =
       this->LocalGenerator->Convert(obj.c_str(),
                                     cmLocalGenerator::START_OUTPUT,
-                                    cmLocalGenerator::SHELL);
+                                    cmLocalGenerator::RESPONSE);
 
     // Roll over to next string if the limit will be exceeded.
     if(this->LengthLimit != std::string::npos &&