[llvm-dev] failing bootstrap: C++11 or greater is required but the compiler does not support c++11

[James Knight via llvm-dev]

On Dec 11, 2016, at 3:33 AM, Eric Fiselier via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> So it seems that libatomic went missing between build #1379 and #1380, so I don't think this is related to the -std=c++11 failure. Instead it seems likely that the compile test for -std=c++11 is failing due to mis-configuring -latomic.
> 
> Can you confirm the bot has libatomic installed?

You shouldn't need it on x86-64. The issue there is that cmake is reporting, incorrectly:
-- Performing Test LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB
-- Performing Test LIBCXX_HAVE_CXX_ATOMICS_WITHOUT_LIB - Failed

despite that previously in the same run, the same test configuring llvm itself worked:
-- Performing Test HAVE_CXX_ATOMICS_WITHOUT_LIB
-- Performing Test HAVE_CXX_ATOMICS_WITHOUT_LIB - Success

I suspect that the flags change has somehow caused *all* compiler invocations to fail, and that results in both the erroneously-failed atomic check and the erroneously-failed std=c++11 check.