vmlinux.lds.h: Fix incomplete .text.exit discards

Enabling CONFIG_GCOV_PROFILE_ALL=y causes linker errors on ARM:

  `.text.exit' referenced in section `.ARM.exidx.text.exit':
  defined in discarded section `.text.exit'

  `.text.exit' referenced in section `.fini_array.00100':
  defined in discarded section `.text.exit'

And related errors on NDS32:

  `.text.exit' referenced in section `.dtors.65435':
  defined in discarded section `.text.exit'

The gcov compiler flags cause certain compiler versions to generate
additional destructor-related sections that are not yet handled by the
linker script, resulting in references between discarded and
non-discarded sections.

Since destructors are not used in the Linux kernel, fix this by
discarding these additional sections.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: Greentime Hu <green.hu@gmail.com>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>