x86/sev: Disable GCOV on noinstr object

With Debian clang version 19.1.7 (3+build5) there are calls to
kasan_check_write() from __sev_es_nmi_complete(), which violates noinstr.  Fix
it by disabling GCOV for the noinstr object, as has been done for previous
such instrumentation issues.

Note that this file already disables __SANITIZE_ADDRESS__ and
__SANITIZE_THREAD__, thus calls like kasan_check_write() ought to be nops
regardless of GCOV. This has been fixed in other patches. However, to avoid
any other accidental instrumentation showing up, (and since, in principle GCOV
is instrumentation and hence should be disabled for noinstr code anyway),
disable GCOV overall as well.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Marco Elver <elver@google.com>
Link: https://patch.msgid.link/20251216-gcov-inline-noinstr-v3-3-10244d154451@google.com