On macOS 11 Big Sur, build fails for 1.32 and master 01dd89c121713beef676837d6e6accb98760ddc4 (Jul 13, 2020) because sys/ioctl.h does not end up included:

    gcc -DHAVE_CONFIG_H -I. -I..  -I../gnu -I../ -I../gnu -I../lib -I../lib -I/usr/local/include   -g -O2 -MT compare.o -MD -MP -MF .deps/compare.Tpo -c -o compare.o compare.c

    compare.c:566:3: error: implicit declaration of function 'ioctl' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
      ioctl (archive, FDFLUSH);
      ^

The logic in [paxutils]/lib/system-ioctl.h appears to include sys/ioctl.h only if sys/mtio.h is found. On Linux (tested on CentOS 7 and Arch) both headers exist and are detected, but, at least on macOS 11 Big Sur, sys/ioctl.h exists while sys/mtio.h does not:

    find /Library/Developer/ -path '*/sys/mtio.h'
    find /Library/Developer/ -path '*/sys/ioctl.h'
    /Library/Developer//CommandLineTools/SDKs/MacOSX11.1.sdk/usr/include/sys/ioctl.h

Should the inclusion checks for these two headers be independent instead? I attached a patch that adds a check for sys/ioctl.h and includes it if found, regardless of the status of sys/mtio.h.

Sidenote: I'm also including an optional patch to checkpoint.c to use system-ioctl.h instead of sys/ioctl.h directly. It's not required to fix the build on macOS, just a proposal.

Attaching patch against 1.32 release (needs autoreconf), and against master. Tested patched on macOS 11 Big Sur, CentOS7, Arch Linux, and Gentoo-Prefix-on-macOS (on latter two tested only patched release 1.32, since master doesn't build with gcc 10, due to Bug #58853). Attaching build logs with and without patch.

Compiler and header info:

    ./configure
    ...
    checking for gcc... gcc
    ...
    checking for sys/gentape.h... no
    checking for sys/inet.h... no
    checking for sys/io/trioctl.h... no
    checking for sys/mtio.h... no
    checking for sys/time.h... yes
    checking for sys/tprintf.h... yes
    checking for sys/tape.h... no

Clang is aliased to gcc on macOS:

    gcc --version
    Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
    Apple clang version 12.0.0 (clang-1200.0.32.28)
    Target: x86_64-apple-darwin20.2.0
    Thread model: posix
    InstalledDir: /Library/Developer/CommandLineTools/usr/bin