[5.1] 54b5a09 Try to confuse GCC to not doing FP brain-damage.

[Poul-Henning Kamp]

commit 54b5a09f00c027da280361b30d32a4ff309ba3ab
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Tue Mar 28 18:44:12 2017 +0000

    Try to confuse GCC to not doing FP brain-damage.
    
    Fixes #1875 (maybe)

diff --git a/bin/varnishd/mgt/mgt_param_tweak.c b/bin/varnishd/mgt/mgt_param_tweak.c
index 12a7a52..b26581e 100644
--- a/bin/varnishd/mgt/mgt_param_tweak.c
+++ b/bin/varnishd/mgt/mgt_param_tweak.c
@@ -52,7 +52,7 @@ static int
 tweak_generic_double(struct vsb *vsb, volatile double *dest,
     const char *arg, const char *min, const char *max, const char *fmt)
 {
-	double u, minv = 0, maxv = 0;
+	volatile double u, minv = 0, maxv = 0;
 
 	if (arg != NULL) {
 		if (min != NULL) {