patch 8.0.0989: ActiveTcl dll name has changed in 8.6.6

Problem:    ActiveTcl dll name has changed in 8.6.6.
Solution:   Adjust the makefile. (Ken Takata)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 1c368ba..52db561 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -340,6 +340,7 @@
 #	  TCL_VER=[TCL version, eg 83, 84] (default is 86)
 #	  TCL_VER_LONG=[Tcl version, eg 8.3] (default is 8.6)
 #	    You must set TCL_VER_LONG when you set TCL_VER.
+#	  TCL_DLL=[TCL dll name, eg tcl86.dll] (default is tcl86.dll)
 ifdef TCL
 ifndef DYNAMIC_TCL
 DYNAMIC_TCL=yes
@@ -350,6 +351,9 @@
 ifndef TCL_VER_LONG
 TCL_VER_LONG = 8.6
 endif
+ifndef TCL_DLL
+TCL_DLL = tcl$(TCL_VER).dll
+endif
 TCLINC += -I$(TCL)/include
 endif
 
@@ -526,7 +530,7 @@
 ifdef TCL
 CFLAGS += -DFEAT_TCL $(TCLINC)
 ifeq (yes, $(DYNAMIC_TCL))
-CFLAGS += -DDYNAMIC_TCL -DDYNAMIC_TCL_DLL=\"tcl$(TCL_VER).dll\" -DDYNAMIC_TCL_VER=\"$(TCL_VER_LONG)\"
+CFLAGS += -DDYNAMIC_TCL -DDYNAMIC_TCL_DLL=\"$(TCL_DLL)\" -DDYNAMIC_TCL_VER=\"$(TCL_VER_LONG)\"
 endif
 endif