Most of the changes are in threads, TLS, dynamic linking, and other
features wasi doesn't yet use, but there are some bug fixes in code
wasi does use.
atanl.c - local changes no longer needed as they've now landed upstream.
include/alltypes.h.in - Upstream now makes FILE a complete type in
pre-C11 mode. For WASI, this level of pre-C11 strictness isn't as
important, and having multiple incompatible definitions of _IO_FILE
that are kept separate only by clever use of translation unit
boundaries can confuse some tools, so stick with the incomplete type.
