bpo-40147: Move the check for duplicate keywords to the compiler

[pablogsal]

https://bugs.python.org/issue40147

[pablogsal]

As a bonus now we print the actual keyword that is repeated.

Before:

❯ python lel.py                       
  File "lel.py", line 1
    f(1, x=2, *(3, 4), x=5)
                       ^
SyntaxError: keyword argument repeated

After:

❯ ./python lel.py  
  File "/home/pablogsal/github/python/master/lel.py", line 1
    f(1, x=2, *(3, 4), x=5)
                       ^
SyntaxError: keyword argument repeated: x

[pablogsal]

CC: @lysnikolaou

[gvanrossum]

Nice! That was simpler than I expected.