Ninja: Substitute <OBJECT> and <CMAKE_C_COMPILER> in depfile flags

Patch by Amine Khaldi!

Also, start using the -MT flag to set a target name for depfiles.
This works around a bug observed in distcc, as explained in the
comment.  Based on a patch by Alexander Usov.

Modules/Compiler/GNU.cmake

@@ -30,7 +30,10 @@ macro(__compiler_gnu lang)
   # in try_compile mode.
   GET_PROPERTY(_IN_TC GLOBAL PROPERTY IN_TRY_COMPILE)
   if(NOT _IN_TC OR CMAKE_FORCE_DEPFILES)
-    set(CMAKE_DEPFILE_FLAGS_${lang} "-MMD -MF <DEPFILE>")
+    # distcc does not transform -o to -MT when invoking the preprocessor
+    # internally, as it ought to.  Work around this bug by setting -MT here
+    # even though it isn't strictly necessary.
+    set(CMAKE_DEPFILE_FLAGS_${lang} "-MMD -MT <OBJECT> -MF <DEPFILE>")
   endif()
 
   # Initial configuration flags.

Source/cmNinjaTargetGenerator.cxx

@@ -331,6 +331,10 @@ cmNinjaTargetGenerator
     depfile = "$out.d";
     cmSystemTools::ReplaceString(depfileFlagsStr, "<DEPFILE>",
                                  depfile.c_str());
+    cmSystemTools::ReplaceString(depfileFlagsStr, "<OBJECT>",
+                                 "$out");
+    cmSystemTools::ReplaceString(depfileFlagsStr, "<CMAKE_C_COMPILER>",
+                       this->GetMakefile()->GetDefinition("CMAKE_C_COMPILER"));
     flags += " " + depfileFlagsStr;
   }
   vars.Flags = flags.c_str();