What version are you running?
RBtools 0.7.5

Windows 10
What steps will reproduce the problem?

Install GNU Diff
Run rbt.exe post

rbt.exe complains about diff not being present

What is the expected output? What do you see instead?
It should work and it doesn't?
What operating system are you using?
Windows 10
Attach the debug out from the command.
C:\Python27\Scripts\rbt-script.py post 1234
GNU diff is required in order to generate diffs. Make sure it is installed

and in the path.
On Windows, you can install this from:

http://gnuwin32.sourceforge.net/packages/diffutils.htm

Please provide any additional information below.
I looked into this and actually it isn't failing to find diff, the execute command in checks is erroring:
'result = execute([diff_cmd, '--version'], ignore_errors=True)'
This seems to be erroring in process.py:

    if sys.platform.startswith('win'):

        # Convert all environment variables to byte strings, so that subprocess

        # doesn't blow up on Windows.

        new_env = dict(

            (six.binary_type(key), six.binary_type(value))

            for key, value in six.iteritems(new_env)

        )

        p = subprocess.Popen(command,    <<<----- HERE

                             stdin=subprocess.PIPE,

                             stdout=subprocess.PIPE,

                             stderr=errors_output,

                             shell=False,

                             universal_newlines=translate_newlines,

                             env=new_env)
Note: setting 'shell' to True in Popen fixes this issue for me!