[C++] Rewrite of the preprocessor.

This rewrite fixes a couple of issues with the pre-processor. It now
supports:
- macros in macro bodies
- stringification of parameters [cpp.stringize]
- the concatenation operator [cpp.concat]
- #include MACRO_HERE
- defined() inside macro bodies used in pp-conditions.

Change-Id: Ifdb78041fb6afadf44f939a4bd66ce2832b8601f
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

tests/auto/cplusplus/preprocessor/data/empty-macro.2.out.cpp

@@ -0,0 +1,31 @@
+# 6 "data/empty-macro.2.cpp"
+class Test {
+private:
+                   Test
+#gen true
+# 3 "data/empty-macro.2.cpp"
+(const
+#gen false
+# 8 "data/empty-macro.2.cpp"
+                   Test
+#gen true
+# 3 "data/empty-macro.2.cpp"
+&);
+#gen false
+# 8 "data/empty-macro.2.cpp"
+                   Test
+#gen true
+# 4 "data/empty-macro.2.cpp"
+&operator=(const
+#gen false
+# 8 "data/empty-macro.2.cpp"
+                   Test
+#gen true
+# 4 "data/empty-macro.2.cpp"
+&);
+#gen false
+# 10 "data/empty-macro.2.cpp"
+public:
+    Test();
+};
+