Code taken from FreeBSD, which implements C11 threads as
wrapper around pthreads. Fix up machine/_threads.h which
is called from newlib's machine-independent threads.h to
match Cygwin's pthreads types.
Add the FreeBSD source files to libc subdir and take
opportunity to define LIBC_OFILES var in Makefile.
Add new symbols to common.din and sort symbols.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
75a669790e