Getting started with Newlib hacking

Hi all:

I would like to make some changes to Newlib. Building or updating a GCC 
toolchain for my embedded target, and flashing the target every time, is 
very time consuming. Therefore, I thought I could somehow make and test 
the Newlib changes on my host PC first.

I took a look at this file:

https://sourceware.org/newlib/README

But it seems outdated. It mentions Newlib version 2.2.0, which is rather 
old now, but more worryingly, option --cygnus is not supported by 
Automake anymore.

Nevertheless, I tried configuring and compiling a few times, but I am 
having no joy. I am getting this error:

/home/rdiez/rdiez/temp/newlib-src/newlib/libc/include/_ansi.h:72:19: 
error: missing binary operator before token "("
  #if __GNUC_PREREQ (3, 1)

Could someone share his/her "./configure" parameters, which are known to 
work?

I am on Ubuntu 16.04, which has GCC 5.4. Is that too old?

I have been looking around further. The top-level configure.ac has code 
for Java and FORTRAN. Is that actually used anywhere?

Autotools-generated files are checked into the Git repository, which 
they normally should not be.

Do I have to be aware of any special considerations when dealing with 
Newlib's build system?

Many thanks in advance,
   rdiez