patch 9.1.0640: Mingw: Makefile can be improved

Problem:  Mingw: Makefile can be improved
Solution: Reduce nesting level, directly check if the '-Wl,--entry'
          option is required (Ken Takata)

closes: #15386

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 7c324fb..d3b04e8 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -1140,15 +1140,14 @@
 $(EXEOBJC): | $(OUTDIR)
 
 ifeq ($(VIMDLL),yes)
- ifneq ($(COVERAGE),yes)
-  ifndef MZSCHEME
-   ifeq ($(ARCH),x86-64)
+ ifneq ($(findstring -nostdlib,$(EXELFLAGS)),)
+  # -Wl,--entry needs to be specified when -nostdlib is used.
+  ifeq ($(ARCH),x86-64)
 EXEENTRYC = -Wl,--entry=wmainCRTStartup
 EXEENTRYG = -Wl,--entry=wWinMainCRTStartup
-   else ifeq ($(ARCH),i686)
+  else ifeq ($(ARCH),i686)
 EXEENTRYC = -Wl,--entry=_wmainCRTStartup
 EXEENTRYG = -Wl,--entry=_wWinMainCRTStartup@0
-   endif
   endif
  endif