Patch is attached.

The change was motivated by including Musl's headers from a project
with -Werror -Wall enabled. I believe Fucshia ran into this, too.  I
couldn't think of a good regression test, in part because warnings are
somewhat compiler specific.  One possible approach would be to enable
-Werror -Wall in the main build, but that runs into issues of which
compilers are supported and what the core developers prefer.  Another
approach would be to only lint the header files - generate a dummy .c
file that includes all the header files and compile it with -Werror.
This is complicated by the "redirection" header files that warn you
should use the canonical version.  Which header files should be
checked?  So for the moment I punted on regression testing.  I mention
this line of thinking in case anyone has some perspective.