.Create a folder named dev-src in your $HOME folder.
.Create a folder named src within dev-src.
Download these to the new src folder.

config
fltk-1.3.4-2.tar.gz
fltk-config
hamlib-config
hamlib3.0.tgz
libpng-1.6.25.tar.gz
libsamplerate-0.1.9.tar.gz
libsndfile-1.0.27.tar.gz
libtool-2.4.6.tar.gz
makebin
pkg-config-0.29.1.tar.gz
portaudio.tar.gz
wget-1.18.tar.gz

untar each compressed file, i.e.

$ tar xzf fltk-1.3.4-2.tar.gz

Make these 4 executable.

$ chmod a+x config
$ chmod a+x hamlib-config
$ chmod a+x fltk-config
$ chmod a+x makebin

Set the environment:

Do the following from the terminal

$ cd
$ ls .bash_profile  (note the dot)

if not found then

$ touch .bash_profile

use the "nano" editor to edit the new or existing file

$ nano .bash_profile

add these lines if they are not already in that file

export PKG_CONFIG=/usr/local/bin/pkg-config
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig

exit and save using the 'control-O', 'control-X' sequence.

Close down the terminal and restart.  Then

$ env

to make sure the changes to local bash environment were made correctly. 

The config file downloaded above is for all but fltk and hamlib,i.e.

Compile and install libraries:

$ cd fltk-1.3.4-2
$ ../fltk-config
$ make
$ sudo make install

$ cd hamlib-3.0
$ ../hamlib-config
$ make
$ sudo make install

$ cd libpng-1.6.25 (& all others)
$ ../config
$ make
$ sudo make install

(Note: wget is very convenient to use from a command line as in
$ wget http://www.w1hkj.com/alpha/flrig/flrig-1.3.34.17.tar.gz
Install it, if desired, the same way as the others above)

To build fldigi:

Download the fldigi source to $Home/dev-src and uncompress it in the same way as the other sources were uncompressed.

Then:

$ cd
$ cd dev-src/fldigi-x.x.x
$ ../makebin

To get a .dmg:

$ make appbundle

Note: The .dmg will be in $Home/dev-src/fldigi-x.x.x/src/ directory.