Gentoo's Bugzilla –
Attachment 565448 Details for
Bug 678052=mail-client/thunderbird-60.5.1 fails to configure if only <sys-devel/clang-7.0.1 is installed but >=sys-devel/llvm-7 is installed: ERROR: The file /usr/lib64/llvm/7/bin/clang returned by `llvm-config -- bindir` does not exist