mconf: Report all unknown cmd line options instead of aborting on first

This is also more consistent with the error message returned by
optinterpreter when it finds unknown command line options.

mesonbuild/coredata.py

@@ -360,7 +360,8 @@ class CoreData:
                 if type(oldval) != type(value):
                     self.user_options[name] = value
 
-    def set_options(self, options):
+    def set_options(self, options, subproject=''):
+        unknown_options = []
         for o in options:
             if '=' not in o:
                 raise MesonException('Value "%s" not of type "a=b".' % o)
@@ -380,7 +381,12 @@ class CoreData:
                 tgt = self.base_options[k]
                 tgt.set_value(v)
             else:
-                raise MesonException('Unknown option %s.' % k)
+                unknown_options.append(k)
+
+        if unknown_options:
+            unknown_options = ', '.join(sorted(unknown_options))
+            sub = 'In subproject {}: '.format(subproject) if subproject else ''
+            raise MesonException('{}Unknown options: "{}"'.format(sub, unknown_options))
 
 def load(build_dir):
     filename = os.path.join(build_dir, 'meson-private', 'coredata.dat')