gcov: add new interface and new formats support

gcov: add new interface and new formats support

A new sysctl interface for passing gcov data back to userspace. The new
interface uses a customised record file format. The new sysctl reuses
original sysctl number but renames the op to gcov_op.

Formats starting from gcc version 3.4 are supported. The code is
rewritten so that a new format can be easily added in the future.
Version specific code is grouped into different files. The format one
needs to use can be picked via Kconfig. The default format is the newest
one.

Userspace programs to handle extracted data will come in a later patch.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>