On windows the temp file cannot be opened a second time while
it is still opened by python. Close the file in python before
asking the compiler to read it.

See https://docs.python.org/3.7/library/tempfile.html#tempfile.NamedTemporaryFile

It is not needed in runtime at all.

This reverts commit 20d0e3b3.

The -stdlib=libc++ flag is no longer supported on Sierra (it is now the
default option). I added a version check that adds the option for macOS
versions below Sierra (10.12) and removed the option otherwise.

Add -Wl,--no-as-needed to Linux builds by default to support Altera FPGAs more easily (#132 on Github)