Searching for sched_yield fails on MinGW.

[xfxyjwf]

The following line causes a ./configure failure on MinGW:

# Need to link against rt on Solaris
AC_SEARCH_LIBS([sched_yield], [rt], [], [AC_MSG_FAILURE([sched_yield was not found on your system])])

It's specific to Solaris and should be moved to m4/acx_check_suncc.m4

[xfxyjwf]

@worr, could you help fix this issue?

[worr]

I'm not sure that that's the right solution here. Technically, sched_yield is required on every platform except Windows. It makes more sense to just disable the check on any Win32 platforms, rather than enable it only for Solaris. On non-Windows, non-Solaris systems, this guarantees the presence of sched_yield

[xfxyjwf]

@worr, your suggestion sounds good to me. Can you help make this change? (i.e., disable the change on Win32).