set the proper preprocessor flag __MINGW32__

src/frontend/plotting/gnuplot.c

@@ -161,7 +161,7 @@ void ft_gnuplot(double *xlims, double *ylims,
     }
 
     /* Set up the file header. */
-#if !defined(__MINGW__) && !defined(_MSC_VER) && !defined(__CYGWIN__)
+#if !defined(__MINGW32__) && !defined(_MSC_VER) && !defined(__CYGWIN__)
     fprintf(file, "set terminal X11 noenhanced\n");
 #elif defined(__CYGWIN__)
 #ifndef EXT_ASC

src/include/ngspice/ngspice.h

@@ -219,7 +219,7 @@ extern double x_atanh(double);
 #endif
 
 #ifndef EXT_ASC
-#if defined(__MINGW__) || defined(_MSC_VER)
+#if defined(__MINGW32__) || defined(_MSC_VER)
 #define fopen newfopen
 extern FILE *newfopen(const char *fn, const char* md);
 #endif

src/misc/util.c

@@ -260,7 +260,7 @@ ngdirname(const char *name)
 
 /* Replacement for fopen, when using wide chars (utf-16) */
 #ifndef EXT_ASC
-#if defined(__MINGW__) || defined(_MSC_VER)
+#if defined(__MINGW32__) || defined(_MSC_VER)
 #undef BOOLEAN
 #include <windows.h>
 FILE *