use isnan instead of _fpclass on non-MSVC compilers
@@ -302,7 +302,7 @@ NCZ_stringconvert1(nc_type srctype, size_t len, char* src, NCjson* jvalue)
snprintf(s,sizeof(s),"%llu",zcvt.uint64v);
} break;
case NC_DOUBLE: {
-#ifdef _WIN32
+#ifdef _MSC_VER
switch (_fpclass(zcvt.float64v)) {
case _FPCLASS_SNAN: case _FPCLASS_QNAN:
strcpy(s,"NaN"); break;
