* BUG: don't mutate list of fake libraries while iterating over it

* BUG: iterate over copy of list

* TST: add build test for build_ext fix (#1)

* TST: add build test for build_ext fix

* TST: clearer test name

* STY: use triple quotes instead of lists of strings

* FIX: check for f77 compiler before test is run

* DOC: add comment explaining that a list copy is necessary

  The new path becomes `build/src.*/numpy/distutils/include/npy_cpu_dispatch_config.h`
  instead of `numpy/core/src/common/_cpu_dispatch.h`.

  The new path allows other projects to re-use the CPU dispatcher
  once we decide to expose the following headers:
    - `numpy/core/src/common/npy_cpu_dispatch.h`
    - `numpy/core/src/common/npy_cpu_features.h`

  '_simd' is a new module to bring the NumPy C SIMD vectorization interface "NPYV"

  The module is designed to be extremely flexible so that it can accommodate any kind
  intrinsics, also to generate a python interface almost similar to the C interface.

  The main purpose of this module is to test NPYV intrinsics in python,
  but still can be used as an effective solution in designing SIMD kernels.

  Also add a new command-line argument `--simd-test` to control of targeted CPU features
  for the `_simd` module.

Co-authored-by: Matti Picus <matti.picus@gmail.com>
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>

  This patch also cleans up `CCompilerOpt` calls in build_ext and build_clib.

see gh-17012 item 12

  - Put `CCompilerOpt` in action through add two command line
    arguments that passed directly to `CCompilerOpt`'s
    parameters which explained as follows:

    * `--cpu-baseline` minimal set of required optimizations,
      default is 'min' which provides the minimum CPU features
      that can safely run on a wide range of users platforms.

    * `--cpu-dispatch` dispatched set of additional optimizations,
      default is 'max-xop-fma4' which enables all CPU features,
      except for AMD legacy features.

    the new arguments can be reached from `build`, `build_clib`,
    `build_ext`, if `build_clib` or `build_ext` are not specified
    by the user the arguments of `build` will be used, which also
    hold the default values.

  - Activate the new compiler dispatcher that comes with `CCompilerOpt`,
    through adding a hock inside `build_clib` and `build_ext`
    that works as a filter taking any C source files ends with
    `.dispatch.c` and pass it directly to `CCompilerOpt` and
    then take returned objects and linked to the final C lib.

  - Add a third command-line argument `--disable-optimization` which
    explicitly disable the whole new infrastructure, also
    It adds a new compiler definition called `NPY_DISABLE_OPTIMIZATION`.

    when `--disable-optimization` is enabled the dispatch-able sources
    that end with `.dispatch.c` will be treated as a normal
    C sources, also due to this disabling any C headers that
    generated by `CCompilerOpt` must guard it with `NPY_DISABLE_OPTIMIZATION`,
    otherwise, it will definitely break the build.

  - New auto-generated C header located at `core/include/numpy/_cpu_dispatch.h`,
    the new header contains all definitions and headers of CPU features that
    enabled according to specified configuration in `--cpu-baseline`
    and `--cpu-dispatch`.

* BUG: relpath fails for different drives on windows

* ENH: always use abspath

* Cleanup unused imports (F401) of mostly standard Python modules,
  or some internal but unlikely referenced modules
* Where internal imports are potentially used, mark with noqa
* Avoid redefinition of imports (F811)

As numpy is Python 3 only, these import statements are now unnecessary
and don't alter runtime behavior.