ctf.c: Fix int/enum implicit cast

ctf.c: Fix int/enum implicit cast

This patch was taken directly from Pedro's branch.

Right now, SET_INT32_FIELD is used to set enum fields.  This works in C,
but not C++.  Therefore, define the new SET_ENUM_FIELD, which casts the
value to the right enum type.

gdb/ChangeLog:

	* ctf.c (SET_ENUM_FIELD): New macro.
	(ctf_read_status): Use it.
	(ctf_read_tp): Use it.