Mescc: avoid `if'.

* module/language/c/lexer.mes (keywords): Produce `If'.
* module/language/c/parser.mes (c-parser): Use `If.'

module/language/c/lexer.mes

@@ -220,7 +220,7 @@
     ("while" . while)
     ("continue" . continue)
     ("default" . default)
-    ("if" . if)
+    ("if" . If)
     ("do" . do)
 
     ;; these aren't exactly keywords, but hey

module/language/c/parser.mes

@@ -61,7 +61,7 @@
            break case continue goto label
            return switch
            for
-           if else
+           If else
            (left: or && ! * / + -)
            (left: bool double float enum void int struct)
            (left: < > <= >=)