Ninja: Partially revert "win fixes: escape back slash/colon, use cd. as cmd.exe nop"

It introduced encoding rules in the wrong place, and broke the
CustomCommand test case.

This reverts commit 7fb2bb3e8b0dc7bc718aadc4ab9a74cb7fdb656e.

Source/CMakeLists.txt

@@ -353,8 +353,9 @@ IF (WIN32)
   ENDIF(NOT UNIX)
 ENDIF (WIN32)
 
-
-SET(SRCS ${SRCS}
+# Ninja only works on UNIX.
+IF(UNIX)
+  SET(SRCS ${SRCS}
     cmGlobalNinjaGenerator.cxx
     cmGlobalNinjaGenerator.h
     cmNinjaTypes.h
@@ -367,8 +368,8 @@ SET(SRCS ${SRCS}
     cmNinjaUtilityTargetGenerator.cxx
     cmNinjaUtilityTargetGenerator.h
     )
-ADD_DEFINITIONS(-DCMAKE_USE_NINJA)
-
+  ADD_DEFINITIONS(-DCMAKE_USE_NINJA)
+ENDIF(UNIX)
 
 # create a library used by the command line and the GUI
 ADD_LIBRARY(CMakeLib ${SRCS})

Source/cmGlobalNinjaGenerator.cxx

@@ -59,7 +59,6 @@ static bool IsIdentChar(char c)
     (c == '_') || (c == '$') || (c == '\\');
 }
 
-
 std::string cmGlobalNinjaGenerator::EncodeIdent(const std::string &ident,
                                                 std::ostream &vars) {
   if (std::find_if(ident.begin(), ident.end(),
@@ -70,19 +69,14 @@ std::string cmGlobalNinjaGenerator::EncodeIdent(const std::string &ident,
     vars << names.str() << " = " << ident << "\n";
     return "$" + names.str();
   } else {
-    return EncodeLiteral(ident);
+    return ident;
   }
 }
 
-
 std::string cmGlobalNinjaGenerator::EncodeLiteral(const std::string &lit)
 {
   std::string result = lit;
   cmSystemTools::ReplaceString(result, "$", "$$");
-  cmSystemTools::ReplaceString(result, ":", "$:");
-#ifdef _WIN32
-  cmSystemTools::ReplaceString(result, "/", "\\");
-#endif
   return result;
 }
 
@@ -206,8 +200,7 @@ cmGlobalNinjaGenerator::WriteCustomCommandBuild(const std::string& command,
   this->AddCustomCommandRule();
 
   cmNinjaVars vars;
-
-  vars["COMMAND"] = EncodeLiteral(command);
+  vars["COMMAND"] = command;
   vars["DESC"] = EncodeLiteral(description);
 
   cmGlobalNinjaGenerator::WriteBuild(*this->BuildFileStream,