TST: Respect compiler customizations

[marv]

Without calling compiler.customize(None) customizations using
environment variables like CC won't be honoured

[charris]

Looks correct to me. @rgommers Comment?

[rgommers]

Yep, that looks correct. Merged, thanks @marv

This is very easy to forgot and leads to subtle bugs that are system-specific. @marv I assume you found this when the tests failed for you? If so, can you add the test output here (helps for searchability for others)?

[marv]

Thanks for the quick merge!

@rgommers: That's right. On Exherbo it's possible to have many (cross-)compilers for various architectures installed side-by-side, in order to prevent subtle bugs/miscompilations we banned unprefixed toolchain executables and only permit host-prefix tools (${host}-${tool}, e.g. x86_64-pc-linux-gnu-cc). The tests here didn't respect the CC specified from the environment and tried to use cc leading to this errors:

======================================================================
ERROR: test_compile1 (test_system_info.TestSystemInfoReading)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/testing/decorators.py", line 147, in skipper_func
    return f(*args, **kwargs)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/tests/test_system_info.py", line 208, in test_compile1
    c.compile([os.path.basename(self._src1)], output_dir=self._dir1)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/ccompiler.py", line 230, in CCompiler_compile
    single_compile(o)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/ccompiler.py", line 194, in single_compile
    self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/unixccompiler.py", line 52, in UnixCCompiler__compile
    raise CompileError(msg)
CompileError: Command "cc -c foo.c -o /var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/tmp1zkQmq/foo.o" failed with exit status 123

======================================================================
ERROR: test_compile2 (test_system_info.TestSystemInfoReading)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/testing/decorators.py", line 147, in skipper_func
    return f(*args, **kwargs)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/testing/decorators.py", line 147, in skipper_func
    return f(*args, **kwargs)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/tests/test_system_info.py", line 227, in test_compile2
    extra_postargs=extra_link_args)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/ccompiler.py", line 230, in CCompiler_compile
    single_compile(o)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/ccompiler.py", line 194, in single_compile
    self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
  File "/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/2.7/test/lib/numpy/distutils/unixccompiler.py", line 52, in UnixCCompiler__compile
    raise CompileError(msg)
CompileError: Command "cc -c bar.c -o /var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/tmpYriDch/bar.o -Wl,-rpath=/var/tmp/paludis/build/dev-python-numpy-1.12.1/temp/tmpYriDch/libbar.so" failed with exit status 123

----------------------------------------------------------------------
Ran 6237 tests in 519.700s

FAILED (KNOWNFAIL=6, SKIP=43, errors=2)