patch 8.0.1351: warning for unused variables building with MinGW

Problem:    Warning for unused variables building with MinGW.
Solution:   Change a few #ifdefs (suggested by John Marriott). Remove
            superfluous checks of FEAT_MBYTE.
diff --git a/src/gui_w32.c b/src/gui_w32.c
index 7610b18..521279e 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -498,9 +498,11 @@
  *
  * These LOGFONT used for IME.
  */
-#ifdef FEAT_MBYTE
+#if defined(FEAT_MBYTE_IME) || defined(GLOBAL_IME)
 /* holds LOGFONT for 'guifontwide' if available, otherwise 'guifont' */
 static LOGFONT norm_logfont;
+#endif
+#ifdef FEAT_MBYTE_IME
 /* holds LOGFONT for 'guifont' always. */
 static LOGFONT sub_logfont;
 #endif
@@ -3361,6 +3363,8 @@
 	font_name = (char_u *)lf.lfFaceName;
 #if defined(FEAT_MBYTE_IME) || defined(GLOBAL_IME)
     norm_logfont = lf;
+#endif
+#ifdef FEAT_MBYTE_IME
     sub_logfont = lf;
 #endif
 #ifdef FEAT_MBYTE_IME
@@ -5794,15 +5798,15 @@
     gui.currSpColor = color;
 }
 
-#if defined(FEAT_MBYTE) && defined(FEAT_MBYTE_IME)
+#ifdef FEAT_MBYTE_IME
 /*
  * Multi-byte handling, originally by Sung-Hoon Baek.
  * First static functions (no prototypes generated).
  */
-#ifdef _MSC_VER
-# include <ime.h>   /* Apparently not needed for Cygwin, MingW or Borland. */
-#endif
-#include <imm.h>
+# ifdef _MSC_VER
+#  include <ime.h>   /* Apparently not needed for Cygwin, MingW or Borland. */
+# endif
+# include <imm.h>
 
 /*
  * handle WM_IME_NOTIFY message
@@ -5954,7 +5958,7 @@
 #endif
 
 /* For global functions we need prototypes. */
-#if (defined(FEAT_MBYTE) && defined(FEAT_MBYTE_IME)) || defined(PROTO)
+#if defined(FEAT_MBYTE_IME) || defined(PROTO)
 
 /*
  * set font to IM.
@@ -6079,7 +6083,7 @@
     return status;
 }
 
-#endif /* FEAT_MBYTE && FEAT_MBYTE_IME */
+#endif /* FEAT_MBYTE_IME */
 
 #if defined(FEAT_MBYTE) && !defined(FEAT_MBYTE_IME) && defined(GLOBAL_IME)
 /* Win32 with GLOBAL IME */