llvm-project

4d21f664 - Be smarter about the GLIBCXX_USE_CXX11_ABI default (#155781)

Be smarter about the GLIBCXX_USE_CXX11_ABI default (#155781) It appears that unconditionally using GLIBCXX_USE_CXX11_ABI=0 is slow on modern libstdc++, while using GLIBCXX_USE_CXX11_ABI=1 breaks old buildbots, so use the compiler default unless asked to do differently.