Clang5 crashing on RPI2 compiling gnome3

[bob prohaska]

Attempts to compile gnome3 on an RPI2 have run hard aground on

<scratch space>:57:6: note: expanded from here
Assertion failed: (0 <= N && N < static_cast<int>(m_byteToColumn.size())), function byteToContainingColumn, file /usr/src/contrib/llvm/tools/clang/lib/Frontend/TextDiagnostic.cpp, line 281.
cc: error: unable to execute command: Abort trap (core dumped)
cc: error: clang frontend command failed due to signal (use -v to see invocation)
FreeBSD clang version 5.0.0 (trunk 308421) (based on LLVM 5.0.0svn)
Target: armv6-unknown-freebsd12.0-gnueabihf
Thread model: posix
InstalledDir: /usr/bin

Does anybody recognize this as a known problem? I seem to recall similar
messages, but those were on clang 4.something.

Is there a workaround?

Thanks for reading,

bob prohaska