add const declaration to newfopen

src/include/ngspice/ngspice.h

@@ -221,7 +221,7 @@ extern double x_atanh(double);
 #ifndef EXT_ASC
 #if defined(__MINGW__) || defined(_MSC_VER)
 #define fopen newfopen
-extern FILE *newfopen(char *fn, char* md);
+extern FILE *newfopen(const char *fn, const char* md);
 #endif
 #endif
 

src/misc/util.c

@@ -264,7 +264,7 @@ ngdirname(const char *name)
 #undef BOOLEAN
 #include <windows.h>
 FILE *
-newfopen(char *fn, char* md)
+newfopen(const char *fn, const char* md)
 {
     if (fn == NULL)
         return NULL;