Fix the build when using mismatching strict ANSI modes with MinGW

Don't use __STRICT_ANSI__ to determine whether a function is available or not
as its value can be different when building the library and the application,
resulting in mysterious link errors.

Instead use the same approach as in aa30a2f97a
and just declare the functions that are available but just not declared in
strict ANSI mode manually.

Closes #15793.

include/wx/wxcrtbase.h

@@ -46,23 +46,12 @@
 #endif
 
 /*
-    Using -std=c++{98,0x} option with mingw32 disables most of standard
-    library extensions, so we can't rely on the presence of common non-ANSI
-    functions, define a special symbol to test for this. Notice that this
-    doesn't need to be done for g++ under Linux where _GNU_SOURCE (which is
-    defined by default) still makes all common extensions available even in
-    ANSI mode.
- */
-#if defined(__MINGW32__) && defined(__STRICT_ANSI__)
-    #define __WX_STRICT_ANSI_GCC__
-#endif
-
-/*
-   a few compilers don't have the (non standard but common) isascii function,
-   define it ourselves for them
+   Traditional MinGW doesn't declare isascii() in strict ANSI mode and we can't
+   declare it here ourselves as it's an inline function, so use our own
+   replacement instead.
  */
 #ifndef isascii
-    #if defined(__WX_STRICT_ANSI_GCC__)
+    #if defined(wxNEEDS_STRICT_ANSI_WORKAROUNDS)
         #define wxNEED_ISASCII
     #endif
 #endif /* isascii */
@@ -140,20 +129,19 @@
 #define wxCRT_StrxfrmW   wcsxfrm
 
 /* Almost all compilers have strdup(), but VC++ and MinGW call it _strdup().
-   And it's not available in MinGW strict ANSI mode nor under Windows CE. */
+   And we need to declare it manually for MinGW in strict ANSI mode. */
 #if (defined(__VISUALC__) && __VISUALC__ >= 1400)
     #define wxCRT_StrdupA _strdup
 #elif defined(__MINGW32__)
-    #ifndef __WX_STRICT_ANSI_GCC__
-        #define wxCRT_StrdupA _strdup
-    #endif
+    wxDECL_FOR_STRICT_MINGW32(char*, _strdup, (const char *))
+    #define wxCRT_StrdupA _strdup
 #else
     #define wxCRT_StrdupA strdup
 #endif
 
-/* most Windows compilers provide _wcsdup() */
-#if defined(__WINDOWS__) && \
-        !(defined(__CYGWIN__) || defined(__WX_STRICT_ANSI_GCC__))
+/* Windows compilers provide _wcsdup() except for (old) Cygwin */
+#if defined(__WINDOWS__) && !defined(__CYGWIN__)
+    wxDECL_FOR_STRICT_MINGW32(wchar_t*, _wcsdup, (const wchar_t*))
     #define wxCRT_StrdupW _wcsdup
 #elif defined(HAVE_WCSDUP)
     #define wxCRT_StrdupW wcsdup
@@ -231,10 +219,13 @@ extern unsigned long android_wcstoul(const wchar_t *nptr, wchar_t **endptr, int
 #if defined(__BORLANDC__)
     #define wxCRT_StricmpA stricmp
     #define wxCRT_StrnicmpA strnicmp
-#elif defined(__VISUALC__)
+#elif defined(__VISUALC__) || defined(__MINGW32__)
+    wxDECL_FOR_STRICT_MINGW32(int, _stricmp, (const char*, const char*))
+    wxDECL_FOR_STRICT_MINGW32(int, _strnicmp, (const char*, const char*, size_t))
+
     #define wxCRT_StricmpA _stricmp
     #define wxCRT_StrnicmpA _strnicmp
-#elif defined(__UNIX__) || (defined(__GNUWIN32__) && !defined(__WX_STRICT_ANSI_GCC__))
+#elif defined(__UNIX__)
     #define wxCRT_StricmpA strcasecmp
     #define wxCRT_StrnicmpA strncasecmp
 /* #else -- use wxWidgets implementation */
@@ -509,7 +500,10 @@ WXDLLIMPEXP_BASE wchar_t * wxCRT_GetenvW(const wchar_t *name);
 #define wxCRT_AtoiA                 atoi
 #define wxCRT_AtolA                 atol
 
-#if defined(wxHAVE_TCHAR_SUPPORT) && !defined(__WX_STRICT_ANSI_GCC__)
+#if defined(wxHAVE_TCHAR_SUPPORT)
+    wxDECL_FOR_STRICT_MINGW32(int, _wtoi, (const wchar_t*))
+    wxDECL_FOR_STRICT_MINGW32(long, _wtol, (const wchar_t*))
+
     #define  wxCRT_AtoiW           _wtoi
     #define  wxCRT_AtolW           _wtol
     /* _wtof doesn't exist */