Revert "selftests/harness: remove use of LINE_MAX"

Patch series "Selftests: Fix compilation warnings due to missing
_GNU_SOURCE definition", v2.

Since kselftest_harness.h introduces asprintf()[1], many selftests have
compilation warnings or errors due to missing _GNU_SOURCE definitions.

The issue stems from a lack of a LINE_MAX definition in Android (see
commit 38c957f0), which is the reason why asprintf() was introduced. 
We tried adding _GNU_SOURCE definitions to more selftests to fix, but
asprintf() may continue to cause problems, and since it is quite late in
the 6.9 cycle, we would like to revert 80921623 first to provide
testing for forks[2].

[1] https://lore.kernel.org/all/20240411231954.62156-1-edliaw@google.com
[2] https://lore.kernel.org/linux-kselftest/ZjuA3aY_iHkjP7bQ@google.com


This patch (of 2):

This reverts commit 80921623.

asprintf() is declared in stdio.h when defining _GNU_SOURCE, but stdio.h
is so common that many files don't define _GNU_SOURCE before including
stdio.h, and defining _GNU_SOURCE after including stdio.h will no longer
take effect, which causes warnings or even errors during compilation in
many selftests.

Revert 'commit 80921623 ("selftests/harness: remove use of LINE_MAX")'
as that came in quite late in the 6.9 cycle.

Link: https://lkml.kernel.org/r/20240509053113.43462-1-tao1.su@linux.intel.com
Link: https://lore.kernel.org/linux-kselftest/ZjuA3aY_iHkjP7bQ@google.com/
Link: https://lkml.kernel.org/r/20240509053113.43462-2-tao1.su@linux.intel.com
Fixes: 80921623

 ("selftests/harness: remove use of LINE_MAX")
Signed-off-by: Tao Su <tao1.su@linux.intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Bongsu Jeon <bongsu.jeon@samsung.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Edward Liaw <edliaw@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Ivan Orlov <ivan.orlov0322@gmail.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Mark Brown <broonie@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Takashi Iwai <tiwai@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>