selftests: link libasan statically for tests with -fsanitize=address

When dynamically linking, Address Sanitizer requires its library to be the
first one to be loaded; this is apparently to ensure that every call to
malloc is intercepted.  If using LD_PRELOAD, those listed libraries will
be loaded before the libraries listed in the program's ELF and will
therefore violate this requirement, leading to the below failure and
output from ASan.

commit 58e2847 ("selftests: line buffer test program's stdout")
modified the kselftest runner to force line buffering by forcing the test
programs to run through `stdbuf`.  It turns out that stdbuf implements
line buffering by injecting a library via LD_PRELOAD.  Therefore selftests
that use ASan started failing.

Fix this by statically linking libasan in the affected test programs,
using the `-static-libasan` option.  Note this is already the default for
Clang, but not got GCC.

Test output sample for failing case:

  TAP version 13
  1..3
  # timeout set to 300
  # selftests: openat2: openat2_test
  # ==4052==ASan runtime does not come first in initial library list;
  you should either link runtime to your application or manually preload
  it with LD_PRELOAD.
  not ok 1 selftests: openat2: openat2_test # exit=1
  # timeout set to 300
  # selftests: openat2: resolve_test
  # ==4070==ASan runtime does not come first in initial library list;
  you should either link runtime to your application or manually preload
  it with LD_PRELOAD.
  not ok 2 selftests: openat2: resolve_test # exit=1

Link: https://lkml.kernel.org/r/20230912135048.1755771-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Fixes: 58e2847 ("selftests: line buffer test program's stdout")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202309121342.97e2f008-oliver.sang@intel.com
Cc: David Hildenbrand <david@redhat.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tom Rix <trix@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/fchmodat2/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
-CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined $(KHDR_INCLUDES)
+CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined -static-libasan $(KHDR_INCLUDES)
 TEST_GEN_PROGS := fchmodat2_test
 
 include ../lib.mk

tools/testing/selftests/openat2/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
-CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
+CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined -static-libasan
 TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test
 
 include ../lib.mk