vs: use CustomBuild instead of CustomBuildStep for custom targets

This allows to view the build step in VS and reuses the same concept that
we use for run targets instead of maintaining two different behaviors.

mesonbuild/backend/vs2010backend.py

@@ -531,8 +531,6 @@ class Vs2010Backend(backends.Backend):
 
     def gen_custom_target_vcxproj(self, target, ofname, guid):
         root = self.create_basic_crap(target, guid)
-        action = ET.SubElement(root, 'ItemDefinitionGroup')
-        customstep = ET.SubElement(action, 'CustomBuildStep')
         # We need to always use absolute paths because our invocation is always
         # from the target dir, not the build root.
         target.absolute_paths = True
@@ -549,9 +547,8 @@ class Vs2010Backend(backends.Backend):
                                              extra_paths=extra_paths,
                                              capture=ofilenames[0] if target.capture else None)
         wrapper_cmd = self.environment.get_build_command() + ['--internal', 'exe', exe_data]
-        ET.SubElement(customstep, 'Command').text = ' '.join(self.quote_arguments(wrapper_cmd))
-        ET.SubElement(customstep, 'Outputs').text = ';'.join(ofilenames)
-        ET.SubElement(customstep, 'Inputs').text = ';'.join([exe_data] + srcs + depend_files)
+        self.add_custom_build(root, 'custom_target', ' '.join(self.quote_arguments(wrapper_cmd)),
+                              deps=[exe_data] + srcs + depend_files, outputs=ofilenames)
         ET.SubElement(root, 'Import', Project=r'$(VCTargetsPath)\Microsoft.Cpp.targets')
         self.generate_custom_generator_commands(target, root)
         self.add_regen_dependency(root)