gcov: add support for GCC 15

gcov: add support for GCC 15

Using gcov on kernels compiled with GCC 15 results in truncated 16-byte
long .gcda files with no usable data.  To fix this, update GCOV_COUNTERS
to match the value defined by GCC 15.

Tested with GCC 14.3.0 and GCC 15.2.0.

Link: https://lkml.kernel.org/r/20251028115125.1319410-1-oberpar@linux.ibm.com
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reported-by: Matthieu Baerts <matttbe@kernel.org>
Closes: https://github.com/linux-test-project/lcov/issues/445
Tested-by: Matthieu Baerts <matttbe@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>