Initial work on an AST dumper.

That will be pretty helpful to understand what's going wrong with
templates.

tests/manual/cplusplus-dump/conf.c++

@@ -0,0 +1,15 @@
+#define __extension__
+#define __context__
+#define __range__
+#define __asm(a...)
+#define __asm__(a...)
+#define   restrict
+#define __restrict
+#define __restrict__
+// #define __weak
+#define __builtin_va_arg(a,b) ((b)0)
+#define __stdcall
+#define __fastcall
+#define __imag__
+#define __real__
+#define __complex__