Gentoo's Bugzilla –
Attachment 591164 Details for
Bug 695726dev-util/perf-5.1.15 USE=clang with sys-devel/clang:9 - util/c++/clang.cpp:74:8: error: ‘class clang::CompilerInstance’ has no member named ‘setVirtualFileSystem’; did you mean ‘getVirtualFileSystem’?