[Bug libstdc++/81797] gcc 7.1.0 fails to build on macOS 10.13 (High Sierra):

[jens4303 at me dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81797

--- Comment #55 from Jens-S. Vöckler <jens4303 at me dot com> ---
Would it be worthwhile to limit it to "darwin" *and* "apfs" on objdir? I am
thinking of something along the lines of 

diskutil info $(stat -f '%Sd' /path/to/objdir) | \
    perl -lane 'print $F[$#F] if /^\s+type/i' 

Once the build system determined "darwin", "diskutil" and "stat" should be
readily available. The expression above returns "apfs" if you need to enact the
patch, and "hfs" if you do not.