Compiler definitions issues

[eyalroz]

There are a few issues with the compiler definitions:

• Some names I've chosen don't exactly fit the definition's actual semantics.
• I really dislike having a pair of definitions for enabling and disabling support for things ... so I think I'll switch to a boolean value which can be defined false (or rather 0) if necessary
• The CMakeLists.txt and printf.c explanatory comments should correspond better.
• The CMake option names and compiler definitions should correspond better.

... and this all will be a first phase to switching to a generated configuration file for building the library.