gcov: remove support for GCC < 4.9

gcov: remove support for GCC < 4.9

Since commit 0bddd227f3dc ("Documentation: update for gcc 4.9
requirement") the minimum supported version of GCC is gcc-4.9.  It's now
safe to remove this code.

Similar to commit 10415533a906 ("gcov: Remove old GCC 3.4 support") but
that was for GCC 4.8 and this is for GCC 4.9.

Link: https://github.com/ClangBuiltLinux/linux/issues/427
Link: https://lkml.kernel.org/r/20201111030557.2015680-1-ndesaulniers@google.com
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>