patch 8.2.4144: cannot load libsodium dynamically

Problem:    Cannot load libsodium dynamically.
Solution:   Support dynamic loading on MS-Windows. (Ken Takata, closes #9554)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index b33d24b..6889a91 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -42,10 +42,10 @@
 #	Sound support: SOUND=yes (default is yes)
 #
 #	Sodium support: SODIUM=[Path to Sodium directory]
-#	 Dynamic built with libsodium
-#	 You need to install the msvc package from
-#	 https://download.libsodium.org/libsodium/releases/
-#	 and package the libsodium.dll with Vim
+#	  DYNAMIC_SODIUM=yes (to load the Sodium DLL dynamically)
+#	  You need to install the msvc package from
+#	  https://download.libsodium.org/libsodium/releases/
+#	  and package the libsodium.dll with Vim
 #
 #
 #	DLL support (EXPERIMENTAL): VIMDLL=yes (default is no)
@@ -384,6 +384,9 @@
 !ifndef SODIUM
 SODIUM = no
 !endif
+!ifndef DYNAMIC_SODIUM
+DYNAMIC_SODIUM = yes
+!endif
 
 !if "$(SODIUM)" != "no"
 ! if "$(CPU)" == "AMD64"
@@ -397,8 +400,13 @@
 
 !if "$(SODIUM)" != "no"
 SOD_INC		= /I "$(SODIUM)\include"
+! if "$(DYNAMIC_SODIUM)" == "yes"
+SOD_DEFS	= -DHAVE_SODIUM -DDYNAMIC_SODIUM
+SOD_LIB		=
+! else
 SOD_DEFS	= -DHAVE_SODIUM
 SOD_LIB		= $(SOD_LIB)\libsodium.lib
+! endif
 !endif
 
 !ifndef NETBEANS