Makefile: Fix double escaping when DEPFILE is used

In commit cfd8a5ac1f (Makefiles: Add support of DEPFILE for
add_custom_command, 2020-12-04, v3.20.0-rc1~237^2~1) we added a
`ConvertToOutputPath` call on a path given to the `depends` field of
`WriteMakeRule`.  The latter already handles escaping for Makefile
syntax.

Fixes: #25554

Source/cmMakefileTargetGenerator.cxx

@@ -1722,9 +1722,8 @@ void cmMakefileTargetGenerator::GenerateCustomRuleFile(
 
   if (!ccg.GetCC().GetDepfile().empty()) {
     // Add dependency over timestamp file for dependencies management
-    auto dependTimestamp = cmSystemTools::ConvertToOutputPath(
-      this->LocalGenerator->MaybeRelativeToTopBinDir(
-        cmStrCat(this->TargetBuildDirectoryFull, "/compiler_depend.ts")));
+    auto dependTimestamp = this->LocalGenerator->MaybeRelativeToTopBinDir(
+      cmStrCat(this->TargetBuildDirectoryFull, "/compiler_depend.ts"));
 
     depends.emplace_back(std::move(dependTimestamp));
   }

Tests/RunCMake/BuildDepends/CustomCommandDepfile.cmake

@@ -24,6 +24,17 @@ add_library(toplib STATIC toplib.c)
 
 add_subdirectory(DepfileSubdir)
 
+set(TEST_SPACE 1)
+if(CMAKE_GENERATOR STREQUAL "Unix Makefiles")
+  execute_process(COMMAND "${CMAKE_MAKE_PROGRAM}" no_such_target --version RESULT_VARIABLE res OUTPUT_VARIABLE out ERROR_VARIABLE out)
+  if(NOT res EQUAL 0 OR NOT out MATCHES "GNU")
+    set(TEST_SPACE 0)
+  endif()
+endif()
+if(TEST_SPACE)
+  add_subdirectory(DepfileSubdirWithSpace)
+endif()
+
 add_custom_command(
   OUTPUT toplib2.c
   DEPFILE toplib2.c.d

Tests/RunCMake/BuildDepends/DepfileSubdirWithSpace/CMakeLists.txt

@@ -0,0 +1,2 @@
+
+add_subdirectory("path with space")

Tests/RunCMake/BuildDepends/DepfileSubdirWithSpace/path with space/CMakeLists.txt

@@ -0,0 +1,9 @@
+
+add_custom_command(OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/dummy.txt"
+  COMMAND ${CMAKE_COMMAND} -E touch "${CMAKE_CURRENT_BINARY_DIR}/dummy.txt"
+  DEPFILE dummy.txt.d
+)
+
+add_custom_target(subdir_space ALL
+  DEPENDS "${CMAKE_CURRENT_BINARY_DIR}/dummy.txt"
+)