Typo fix.
Fix using emcc -E.

We don't want to pass this extra flag to emcc as it breaks when
doing EMCONFIGURE_JS=1 emconfigure ./configure ...
Expand on the instructions for building Python.
Update libc headers to use musl headers.
Update to work with new libc headers.
Fix other.test_embind & other.test_static_link.
Fix time tests.
Add __va_copy as a compat/stdarg.h
Fix fpclassify with musl libc headers.

musl defines __fpclassify, __fpclassifyf, __fpclassifyl while
the old headers used __fpclassifyd for double rather than
__fpclassify.
Provide better impl of __assert_fail().
Bump version for new libc headers.
Emscripten requires different #s for stdio fds.
Handle fpclassify and signbit for long double.
Fix sockaddr struct definitions for musl.
gethostbyname_r update.

* gethostbyname_r is now the 6 arg version.
* Make enet use the right code path (this should be upstreamed).
* Add a compat header to make these declarations visible to all without
  extra compilation flags.
Change various 64 bit typedefs over to 32 bit.

This also removes all of the changes that were needed for those
typedefs to be 64 bit.
Correctly note musl provenance and differences.
Update to musl-0.9.13 headers.
Incorrect return type on a compat header.

This was exposed by the update to musl 0.9.13 which now has a
prototype for this function.
Skip test_math unless using ta2

isfinite and friends require ta2 with musl headers.