-D_GLIBCXX_USE_CXX11_ABI=0 cflags?

Hi, I wonder how to set -D_GLIBCXX_USE_CXX11_ABI=1 when building apex. I got this error when using syncbn:

Warning:  using Python fallback for SyncBatchNorm, possibly because apex was installed without --cuda_ext.  The exception raised when attempting t
o import the cuda backend was:  /usr/lib/python3.7/site-packages/syncbn.cpython-37m-x86_64-linux-gnu.so: undefined symbol: _ZN3c105ErrorC1ENS_14So
urceLocationERKSs

and then I got:

$ c++filt _ZN3c105ErrorC1ENS_14SourceLocationERKSs
c10::Error::Error(c10::SourceLocation, std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)

It is said related to -D_GLIBCXX_USE_CXX11_ABI according to this post.
Also, I check ABI by:

$ strings /usr/lib/python3.7/site-packages/torch/lib/libtorch.so|grep ABI
CXXABI_1.3.8
CXXABI_1.3.5
CXXABI_1.3.7
CXXABI_1.3.3
CXXABI_1.3

$ strings /usr/lib/python3.7/site-packages/syncbn.cpython-37m-x86_64-linux-gnu.so|grep ABI
CXXABI_1.3
CXXABI_1.3.3
CXXABI_1.3.5

A solution to this is compile apex with -D_GLIBCXX_USE_CXX11_ABI=1. So, how could I do that?

Start with the apex installation/build entry point and the --cuda_ext option mentioned in the report, then trace how compiler flags are passed to the extension. Reproduce the syncbn import failure and verify that the resulting extension loads without the reported C++ ABI symbol error.