title: Complie riscv-gnu-toolchain on MacOS Error
body: <p>I compile gnu-tool-chain on my Mac, and get some error message<br />
  I'm in the riscv-gnu-toolchain root directory, and</p>
  <pre><code>./configure --prefix=/usr/local/opt/riscv-gnu-toolchain
  make
  </code></pre>
  <p>I get</p>
  <pre><code>...
  /Volumes/CaseSensitive/riscv-gnu-toolchain/riscv-gdb/readline/rltty.c:83:7: error:
        implicit declaration of function 'ioctl' is invalid in C99
        [-Werror,-Wimplicit-function-declaration]
    if (ioctl (tty, TIOCGWINSZ, &amp;w) == 0)
        ^
  /Volumes/CaseSensitive/riscv-gnu-toolchain/riscv-gdb/readline/rltty.c:720:3: error:
        implicit declaration of function 'ioctl' is invalid in C99
        [-Werror,-Wimplicit-function-declaration]
    ioctl (fildes, TIOCSTART, 0);
    ^
  /Volumes/CaseSensitive/riscv-gnu-toolchain/riscv-gdb/readline/rltty.c:759:3: error:
        implicit declaration of function 'ioctl' is invalid in C99
        [-Werror,-Wimplicit-function-declaration]
    ioctl (fildes, TIOCSTOP, 0);
    ^
  3 errors generated.
  make[3]: *** [rltty.o] Error 1
  make[2]: *** [all-readline] Error 2
  make[1]: *** [all] Error 2
  make: *** [stamps/build-gdb-newlib] Error 2
  </code></pre>
  <p>My MacOS version is 10.15.7.
  Should I add some headers file in somewhere?</p>