`make check` failures on test_legacy.sh and test_16threads.sh

[sjuxax]

I get failures on two tests when I run make check: test_legacy and test_16threads.

Compiling on an up-to-date ArchLinux. Tried with make -j16 first and retried with make -j1 with no change. Built off today's HEAD.

$ git rev-parse HEAD
26901e5078876f42bbbfbf3b0fe6bcbe81f787ee

$ g++ --version
g++ (GCC) 7.1.1 20170516
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

CXXFLAGS (CFLAGS are identical)

$ echo $CXXFLAGS
-march=native -mtune=native -O2 -pipe -fstack-protector-strong -mavx2

$ uname -a
Linux kvm_master 4.11.3-1-ARCH #1 SMP PREEMPT Sun May 28 10:40:17 CEST 2017 x86_64 GNU/Linux

Found a similar bug report on Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=853479

lepton-test-suite.log.txt lepton_build.stdout.log.txt lepton_build.stderr.log.txt

[danielrh]

Turns out it's a gcc bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81015 bad codegen for builtin_clz will avoid using that for gcc 7 series... that's really scary