C99 functions are only available in MSVC 2013 and newer. Still needs testing!

src/include/ngspice/ngspice.h

@@ -158,6 +158,8 @@ extern void SetAnalyse(char *Analyse, int Percent);
 #if defined (_MSC_VER)
 #include <direct.h>
 #include <process.h>
+/* C99 not available before VC++ 2013) */
+#if (_MSC_VER < 1800)
 #define trunc x_trunc
 extern double x_trunc(double);
 #define nearbyint x_nearbyint
@@ -168,6 +170,7 @@ extern double x_asinh(double);
 extern double x_acosh(double);
 #define atanh x_atanh
 extern double x_atanh(double);
+#endif
 #define strdup _strdup
 #define unlink _unlink
 #define fileno _fileno