Strictly detects armhf via compiler definitions,
  to avoid building neon objects on arch armel even when
  the compiler supports armv7 features on it.

Introduce numpy.core.setup_common.NPY_CXX_FLAGS

Group all C++ flags in one location.

This avoids redundancy and makes sure we test the flags we use, and use the
flags we test.

Fix #21302

ENH: Use SVML for f64 exp and log 

Work around for a bug in gcc compiler. When using several kmask
variables __mmask16/__mmask8, the compiler sometimes uses %mmx registers
to save them on to the stack which corrupts the x87 stack.

Actual c++ification.

Also fix a slight bug in numpy/distutils/ccompiler_opt.py when intermediate
directory is missing.

Here are two modifications:

The first one is the inclusion of markdown fence blocks in the middle of
RST. While this is not really a problem for current documentation as
this is a private function, it still makes other RST parser choke on
this.

In particular this is seen as a tile as it is a text line followed by
a line of only backticks, and that makes my new project to show better
docstrings in Jupyter fails.

I can locally exclude this function, but while not fix it to show good
examples ?

Second, while grepping for triple backticks I found that there are a
stray one in another place.