fixing libmudflap configuration

[Per Bothner]

Frank Ch. Eigler wrote:

>>The next problem was the wrappers in mf-hooks2.c including
>>lots of missing header files.  The patch to configure.in
>>and mf-hooks2.c is one solution, but perhaps not the right
>>one.
>
> It is a part of the solution.

Ok to check in this part of the patch too, assuming it passes
a linux-native bootstrap?

>>And indeed, mingw doesn't have pthread.h, but I don't know
>>what the fallback is.
> 
> In this case, the configury is supposed to arrange things so that
> libmudflapth (th == threaded) is not built at all.

< AM_CONDITIONAL(LIBMUDFLAPTH, [test "x$ac_have_pthread_h" != ""])
 > AM_CONDITIONAL(LIBMUDFLAPTH, [test "$ac_have_pthread_h" != ""])
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/