Created attachment 167145 [details]
make & truss output

I'm using portupagrade to update ports, and sometimes configuring devel/m4 hangs on the "checking dup2":
{...}
checking whether dup2 works... ^C0.006u 0.027s 6:42.60 0.0%	3316+612k 37+0io 0pf+0w

truss shows the following:
{...}
fcntl(1,F_SETFD,FD_CLOEXEC)			 = 0 (0x0)
dup2(0x1,0x1,0x1,0x18,0x300,0x7fffffffd6ef)	 = 1 (0x1)
fcntl(1,F_GETFD,)				 = 1 (0x1)
close(0)					 = 0 (0x0)
dup2(0x0,0x0,0x1,0x18,0x300,0x7fffffffd6ef)	 ERR#9 'Bad file descriptor'
^C^C^C^C^C^C^C^C^CKilled
0.000u 0.003s 117:42:18.87 0.0%	0+0k 0+0io 0pf+0w

Process "conftest" hangs in a D state.