MFC r357223:

Merge r357222 from the clang1000-import branch:

Fix the following -Werror warning from clang 10.0.0 in rbootd:

libexec/rbootd/rmpproto.c:335:49: error: multiple unsequenced modifications to 'filename' [-Werror,-Wunsequenced]

filename = (filename = strrchr(filepath,'/'))? ++filename: filepath;
         ~                                     ^