selftests/vm: make MADV_POPULATE_(READ|WRITE) use in-tree headers

The madv_populate selftest currently builds with a warning when the
local installed headers (via the distribution) don't include
MADV_POPULATE_READ and MADV_POPULATE_WRITE. The warning is correct,
because the test cannot locate the necessary header.

The reason is that the in-tree installed headers (usr/include) have a
"linux" instead of a "sys" subdirectory.

Including "linux/mman.h" instead of "sys/mman.h" doesn't work (e.g.,
mmap() and madvise() are not defined that way). The only thing that
seems to work is including "linux/mman.h" in addition to "sys/mman.h".

We can get rid of our availability check and simplify.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: David Hildenbrand <[e-mail]>
Reported-by: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/vm/madv_populate.c

···
 #include <unistd.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <linux/mman.h>
 #include <sys/mman.h>
 
 #include "../kselftest.h"
-
-#if defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE)
 
 /*
  * For now, we're using 2 MiB of private anonymous memory for all tests.
···
 				   err, ksft_test_num());
 	return ksft_exit_pass();
 }
-
-#else /* defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE) */
-
-#warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition"
-
-int main(int argc, char **argv)
-{
-	ksft_print_header();
-	ksft_exit_skip("MADV_POPULATE_READ or MADV_POPULATE_WRITE not defined\n");
-}
-
-#endif /* defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE) */