hardening: simplify CONFIG_CC_HAS_COUNTED_BY

hardening: simplify CONFIG_CC_HAS_COUNTED_BY

Simplifies CONFIG_CC_HAS_COUNTED_BY by removing the build test and
relying solely on gcc/clang version numbering (GCC_VERSION >= 150100 and
CLANG_VERSION >= 190103).

The build test was used to allow unreleased gcc 15.0 builds to use the
__counted_by attribute. Now that gcc 15.1.0 has been released, this is
not needed anymore. Note: This will disable __counted_by on unreleased
gcc 15.0 builds.

clang version support for __counted_by remains unchanged.

Link: https://lore.kernel.org/all/Zw8iawAF5W2uzGuh@archlinux/T/#m204c09f63c076586a02d194b87dffc7e81b8de7b
Link: https://lore.kernel.org/r/20241029140036.577804-2-kernel@jfarr.cc
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Jan Hendrik Farr <kernel@jfarr.cc>
Link: https://lore.kernel.org/r/20250430184231.671365-2-kernel@jfarr.cc
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <kees@kernel.org>