selftests: Compile kselftest headers with -D_GNU_SOURCE

Add the -D_GNU_SOURCE flag to KHDR_INCLUDES so that it is defined in a
central location.

Commit 809216233555 ("selftests/harness: remove use of LINE_MAX")
introduced asprintf into kselftest_harness.h, which is a GNU extension
and needs _GNU_SOURCE to either be defined prior to including headers or
with the -D_GNU_SOURCE flag passed to the compiler.

Fixed up commit log:
Shuah Khan <[email protected]>

Fixes: 809216233555 ("selftests/harness: remove use of LINE_MAX")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Signed-off-by: Edward Liaw <[email protected]>
Reviewed-by: Muhammad Usama Anjum <[email protected]>
Reviewed-by: Mark Brown <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

0 files changed, 0 insertions, 0 deletions