Support compilation on macOS 11.x

[ravenzachary]

Support (and document steps for) compilation of the code on macOS 11.x.

[ravenzachary]

• ./make.all fails due to the following error numerous times:
  fatal error: 'malloc.h' file not found

A Google search results in a recommendation to find and replace all malloc.h with:

"The malloc.h is deprecated and should not be used. It contains some non-standard functions too. If you want to use malloc, then include stdlib.h. Not even the C89 standard mentions malloc.h"

I fixed this problem when I compiled the code on Linux. I need to go back and see if macOS generates additional errors after fixing this one.

[mdhender]

Does macOS 11 using the clang tool chain?

[ravenzachary]

masOS includes clang if you install Xcode and the optional Command Line Tools.

The other common method to compile POSIX apps on macOS is to install MacPorts, Homebrew, Fink, or pkgin.

Ideally, I will document the steps for all approaches.