Starting with GCC 5, the __builtin_isnan() fucntion requires proper overloaded types, even in C:
* osptransapi.c:1040:13: error: non-floating-point argument in call to function ‘__builtin_isnan’
*              OSPM_ISNAN(metrics.mean, tnisnan);
See also:
https://bugs.gentoo.org/show_bug.cgi?id=581058

--- a/src/osptransapi.c
+++ b/src/osptransapi.c
@@ -983,7 +983,7 @@
             /* sample mean - have to cast Samples to a float to get some precision on the mean */
             mean = ((metrics.mean * currnumber) + (ospvMean * ospvSamples)) / (float)metrics.samples;
 
-            OSPM_ISNAN(metrics.mean, tnisnan);
+            OSPM_ISNAN((double)metrics.mean, tnisnan);
 
             if (tnisnan) {
                 errcode = OSPC_ERR_TRAN_INVALID_CALC;