ZynAddSubFX: fixed win32 compilation of FLTK and MXML

Some platform-specific constants got renamed during sed-mass-replace.
Fix this by reverting concerning constant names.
(cherry picked from commit 78536d9065)

plugins/zynaddsubfx/fltk/src/fl_dnd_win32.cxx

@@ -343,7 +343,7 @@ public:
   }
 
   HRESULT __stdcall Next(ULONG celt, FORMATETC * rgelt, ULONG *pceltFetched) {
-    if (n > 0) return S_false;
+    if (n > 0) return S_FALSE;
     for (ULONG i = 0; i < celt; i++) {
       n++;
       rgelt->cfFormat = CF_HDROP;
@@ -358,7 +358,7 @@ public:
 
   HRESULT __stdcall Skip(ULONG celt) {
     n += celt;
-    return  (n == 0) ? S_OK : S_false;
+    return  (n == 0) ? S_OK : S_FALSE;
   }
 
   HRESULT __stdcall Reset(void) {

plugins/zynaddsubfx/mxml/mxml-private.c

@@ -208,7 +208,7 @@ DllMain(HINSTANCE hinst,		/* I - DLL module handle */
   { 
     case DLL_PROCESS_ATTACH :		/* Called on library initialization */
         if ((_mxml_tls_index = TlsAlloc()) == TLS_OUT_OF_INDEXES) 
-          return (false); 
+          return (FALSE); 
         break; 
 
     case DLL_THREAD_DETACH :		/* Called when a thread terminates */
@@ -227,7 +227,7 @@ DllMain(HINSTANCE hinst,		/* I - DLL module handle */
         break; 
   } 
 
-  return (true);
+  return (TRUE);
 }