[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/identifier-expansion.3.out.cpp

@@ -0,0 +1,23 @@
+# 8 "data/identifier-expansion.3.cpp"
+enum op_code {
+#gen true
+# 6 "data/identifier-expansion.3.cpp"
+op_ADD, op_SUB,
+#gen false
+# 10 "data/identifier-expansion.3.cpp"
+};
+
+static const char *names[] = {
+#gen true
+# 2 "data/identifier-expansion.3.cpp"
+            "ADD"
+
+
+,
+# 3 "data/identifier-expansion.3.cpp"
+ "SUB"
+
+,
+#gen false
+# 14 "data/identifier-expansion.3.cpp"
+};