chThread.h: unconditionally use libc11 threads

__STDC_NO_THREADS__ doesn't always get correctly defined. Why the *hell* did
someone think it was a good idea to define a macro to indicate *lack* of
support? By this logic I should compile with GCC 2.95 and since
__STDC_NO_THREADS__ isn't defined, it supports C11 threads, right?

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Makefile: unbreak linkage on Cygwin

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
libc11: unbreak build on Cygwin

Signed-off-by: Steven Noonan <steven@uplinklabs.net>