Use absolute paths for dep files in Visual Studio.

mesonbuild/backend/backends.py

@@ -568,7 +568,10 @@ class Backend():
                 elif '@DEPFILE@' in i:
                     if target.depfile is None:
                         raise MesonException('Custom target %s has @DEPFILE@ but no depfile keyword argument.' % target.name)
-                    dfilename = os.path.join(self.get_target_private_dir(target), target.depfile)
+                    if absolute_paths:
+                        dfilename = os.path.join(self.get_target_private_dir_abs(target), target.depfile)
+                    else:
+                        dfilename = os.path.join(self.get_target_private_dir(target), target.depfile)
                     i = i.replace('@DEPFILE@', dfilename)
                 elif '@PRIVATE_OUTDIR_' in i:
                     match = re.search('@PRIVATE_OUTDIR_(ABS_)?([-a-zA-Z0-9.@:]*)@', i)