BUG: distutils, add compatiblity python parallelization

Python 3.5 also added build parallelization at the extension level
instead of the file leve numpy uses.
This causes two problems:

- numpy.distutils is not threadsafe with duplicated source files
When source files are duplicated in multiple extensions the output
objects are overwritten which can truncate in a parallel context.
This is fixed by keeping track of the files being worked on and wait
for completion if another thread is already using the object name.

- The parallelization on two nested levels causes oversubscription.
When building multiple extensions with multiple source files the number
of jobs running is multiplied.
This is fixed by adding a semaphore that limits the number of jobs numpy
starts to the defined amount.

closes gh-7139

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