Fix failing rpass-valgrind test

[nrc]

This is blocking turning valgrind tests back on.

exit-flushes.rs is apparently the culprit.

cc @edunham, @nikomatsakis, @alexcrichton

(p-high since it is blocking fixing our test infra)

[nrc]

cc @nagisa

[nrc]

cc @rust-lang/compiler (I wish labelling T-compiler did this automatically)

[alexcrichton]

What's the actual errors here? Running valgrind without flags reports:

$ valgrind ./exit-flushes
==15994== Memcheck, a memory error detector
==15994== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==15994== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==15994== Command: ./exit-flushes
==15994== 
==15994== 
==15994== HEAP SUMMARY:
==15994==     in use at exit: 32 bytes in 1 blocks
==15994==   total heap usage: 52 allocs, 51 frees, 3,200 bytes allocated
==15994== 
==15994== LEAK SUMMARY:
==15994==    definitely lost: 0 bytes in 0 blocks
==15994==    indirectly lost: 0 bytes in 0 blocks
==15994==      possibly lost: 0 bytes in 0 blocks
==15994==    still reachable: 32 bytes in 1 blocks
==15994==         suppressed: 0 bytes in 0 blocks
==15994== Rerun with --leak-check=full to see details of leaked memory
==15994== 
==15994== For counts of detected and suppressed errors, rerun with: -v
==15994== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

And running with more flags:

$ valgrind --show-leak-kinds=all --leak-check=full ./exit-flushes
==16010== Memcheck, a memory error detector
==16010== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==16010== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==16010== Command: ./exit-flushes
==16010== 
==16010== 
==16010== HEAP SUMMARY:
==16010==     in use at exit: 32 bytes in 1 blocks
==16010==   total heap usage: 52 allocs, 51 frees, 3,200 bytes allocated
==16010== 
==16010== 32 bytes in 1 blocks are still reachable in loss record 1 of 1
==16010==    at 0x4C2CC70: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16010==    by 0x4E3868F: _dlerror_run (dlerror.c:141)
==16010==    by 0x4E380C0: dlopen@@GLIBC_2.2.5 (dlopen.c:87)
==16010==    by 0x115427: dynamic_lib::_$LT$impl$GT$::open::h18d9049daa783e54g0d (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x11E675: sys::thread::_$LT$impl$GT$::new::h12092075689a77b6yFw (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x11BB4F: process::_$LT$impl$GT$::wait_with_output::h9de87472d42d007c8Qm (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x11B86C: process::_$LT$impl$GT$::output::hc2dfccaa9143d1c54Cm (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x11034A: main::h82a74a745ccbaed7iaa (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x1256B4: sys_common::unwind::try::try_fn::h5598476508523168281 (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x1229C8: __rust_try (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x125356: rt::lang_start::he15236a7da0e712coox (in /home/alex/code/rust4/exit-flushes)
==16010==    by 0x114329: main (in /home/alex/code/rust4/exit-flushes)
==16010== 
==16010== LEAK SUMMARY:
==16010==    definitely lost: 0 bytes in 0 blocks
==16010==    indirectly lost: 0 bytes in 0 blocks
==16010==      possibly lost: 0 bytes in 0 blocks
==16010==    still reachable: 32 bytes in 1 blocks
==16010==         suppressed: 0 bytes in 0 blocks
==16010== 
==16010== For counts of detected and suppressed errors, rerun with: -v
==16010== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

(which looks benign)

[nagisa]

Happens with simple check-stage1-rpass-valgrind

---- [run-pass-valgrind] run-pass-valgrind/exit-flushes.rs stdout ----

error: test run failed!
status: exit code: 100
command: /usr/bin/valgrind --error-exitcode=100 --fair-sched=try --quiet --soname-synonyms=somalloc=NONE --suppressions=/home/nagisa/Documents/rust/rust/src/etc/x86.supp --tool=memcheck --leak-check=full x86_64-unknown-linux-gnu/test/run-pass-valgrind/exit-flushes.stage1-x86_64-unknown-linux-gnu
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
==28178== 288 bytes in 1 blocks are possibly lost in loss record 2 of 2
==28178==    at 0x4C2A987: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==28178==    by 0x4011841: allocate_dtv (in /usr/lib/ld-2.22.so)
==28178==    by 0x401221D: _dl_allocate_tls (in /usr/lib/ld-2.22.so)
==28178==    by 0x5CDB044: pthread_create@@GLIBC_2.2.5 (in /usr/lib/libpthread-2.22.so)
==28178==    by 0x4F4E989: sys::thread::_$LT$impl$GT$::new::h18c8e1383a16a102QFw (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F4BD67: thread::_$LT$impl$GT$::spawn::h8240507308132532220 (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F4AE15: thread::spawn::h8206638966982322642 (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F4341D: process::_$LT$impl$GT$::wait_with_output::read::h16290293560351911718 (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F4042A: process::_$LT$impl$GT$::wait_with_output::h149e8dca7ba9fec96Pm (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F402AD: process::_$LT$impl$GT$::output::_$LT$closure$GT$::closure.38650 (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F40128: result::_$LT$impl$GT$::and_then::and_then::h12745603337970662170 (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178==    by 0x4F40077: process::_$LT$impl$GT$::output::h85147110d45a11184Bm (in /home/nagisa/Documents/rust/rust/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-71b07a99.so)
==28178== 
------------------------------------------

[alexcrichton]

Ah I think that may have been fixed by #29897

[nrc]

Confirmed - we now pass all rpass-valgrind tests.