vs: use regular quotes instead of '"' in Generator commands

Seems like CustomBuild does not like '"', but works just fine with
regular quotes.

mesonbuild/backend/vs2010backend.py

@@ -129,10 +129,9 @@ class Vs2010Backend(backends.Backend):
                     args = self.replace_outputs(args, target_private_dir, outfiles_rel)
                     args = [x.replace("@SOURCE_DIR@", self.environment.get_source_dir()).replace("@BUILD_DIR@", target_private_dir)
                             for x in args]
-                    fullcmd = exe_arr + self.replace_extra_args(args, genlist)
-                    command = ' '.join(self.special_quote(fullcmd))
+                    cmd = exe_arr + self.replace_extra_args(args, genlist)
                     cbs = ET.SubElement(idgroup, 'CustomBuild', Include=infilename)
-                    ET.SubElement(cbs, 'Command').text = command
+                    ET.SubElement(cbs, 'Command').text = ' '.join(self.quote_arguments(cmd))
                     ET.SubElement(cbs, 'Outputs').text = ';'.join(outfiles)
         return generator_output_files, custom_target_output_files, custom_target_include_dirs
 
@@ -331,8 +330,8 @@ class Vs2010Backend(backends.Backend):
         directories = os.path.normpath(target.subdir).split(os.sep)
         return os.sep.join(['..'] * len(directories))
 
-    def special_quote(self, arr):
-        return ['"%s"' % i for i in arr]
+    def quote_arguments(self, arr):
+        return ['"%s"' % i for i in arr]
 
     def create_basic_crap(self, target):
         project_name = target.name
@@ -404,8 +403,7 @@ class Vs2010Backend(backends.Backend):
         # from the target dir, not the build root.
         target.absolute_paths = True
         (srcs, ofilenames, cmd) = self.eval_custom_target_command(target, True)
-        cmd_templ = '''"%s" ''' * len(cmd)
-        ET.SubElement(customstep, 'Command').text = cmd_templ % tuple(cmd)
+        ET.SubElement(customstep, 'Command').text = ' '.join(self.quote_arguments(cmd))
         ET.SubElement(customstep, 'Outputs').text = ';'.join(ofilenames)
         ET.SubElement(customstep, 'Inputs').text = ';'.join(srcs)
         ET.SubElement(root, 'Import', Project='$(VCTargetsPath)\Microsoft.Cpp.targets')