If you occur problem in compilation, check the file and symlink.
/usr/ports/devel/llvm80 # make
(...)
===> Building for llvm80-8.0.1_3 ninja: error: '/usr/local/lib/libexecinfo.so', needed by 'bin/lldb-argdumper', missing and no known rule to make it ===> Compilation failed unexpectedly.
% ls -l /usr/local/lib/libexecinfo.so lrwxr-xr-x 1 root wheel 16 May 19 2014 /usr/local/lib/libexecinfo.so -> libexecinfo.so.1
% which /usr/local/lib/libexecinfo.so /usr/local/lib/libexecinfo.so: Command not found.
% file /usr/local/lib/libexecinfo.so /usr/local/lib/libexecinfo.so: broken symbolic link to libexecinfo.so.1
# unlink /usr/local/lib/libexecinfo.so