[6.0] aa797877e Fix compiling under epel6

[Dridi Boukelmoune]

commit aa797877e7d9feaf584ab56a57a6e96350dabb09
Author: Federico G. Schwindt <fgsch at lodoss.net>
Date:   Fri Apr 27 00:07:14 2018 +0100

    Fix compiling under epel6
    
    Reported by ingvar

diff --git a/bin/varnishtest/vtc_process.c b/bin/varnishtest/vtc_process.c
index 7ab093b90..5e3816bca 100644
--- a/bin/varnishtest/vtc_process.c
+++ b/bin/varnishtest/vtc_process.c
@@ -485,7 +485,7 @@ process_stdout(const struct vev *ev, int what)
 		vtc_dump(p->vl, 4, "stdout", buf, i);
 	else if (p->log == 3)
 		vtc_hexdump(p->vl, 4, "stdout", buf, i);
-	(void)write(p->f_stdout, buf, i);
+	assert(write(p->f_stdout, buf, i) == i);
 	AZ(pthread_mutex_lock(&p->mtx));
 	teken_input(p->tek, buf, i);
 	AZ(pthread_mutex_unlock(&p->mtx));
@@ -510,7 +510,7 @@ process_stderr(const struct vev *ev, int what)
 	p->stderr_bytes += i;
 	AZ(pthread_mutex_unlock(&p->mtx));
 	vtc_dump(p->vl, 4, "stderr", buf, i);
-	(void)write(p->f_stderr, buf, i);
+	assert(write(p->f_stderr, buf, i) == i);
 	return (0);
 }