Allow using debug help API with non-MSVC compilers

MinGW64 and TDM-GCC come with imagehlp.h and can compile the code using debug
help API too, so enable wxUSE_DBGHELP when using these compilers by default
and also allow enabling it via a configure option.

include/wx/msw/debughlp.h

@@ -10,8 +10,11 @@
 #ifndef _WX_MSW_DEBUGHLPH_H_
 #define _WX_MSW_DEBUGHLPH_H_
 
-#include "wx/dynlib.h"
+#include "wx/defs.h"
 
+#if wxUSE_DBGHELP
+
+#include "wx/dynlib.h"
 #include "wx/msw/wrapwin.h"
 
 #ifdef __VISUALC__
@@ -31,26 +34,6 @@
 
 #include "wx/msw/private.h"
 
-// wxUSE_DBGHELP can be predefined on the compiler command line to force using
-// dbghelp.dll even if it's not detected or, on the contrary, avoid using even
-// if it's available.
-#ifndef wxUSE_DBGHELP
-    // The only compiler which is known to have the necessary headers is MSVC.
-    #ifdef __VISUALC__
-        // MSVC7.1 shipped with API v9 and we don't support anything earlier
-        // anyhow.
-        #if API_VERSION_NUMBER >= 9
-            #define wxUSE_DBGHELP 1
-        #else
-            #define wxUSE_DBGHELP 0
-        #endif
-    #else
-        #define wxUSE_DBGHELP 0
-    #endif
-#endif
-
-#if wxUSE_DBGHELP
-
 /*
 
 The table below shows which functions are exported by dbghelp.dll.