build/msvc: Move include into unix_defs.h

src/nvim/os/os_defs.h

@@ -4,7 +4,6 @@
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <sys/param.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 

src/nvim/os/unix_defs.h

@@ -1,9 +1,10 @@
 #ifndef NVIM_OS_UNIX_DEFS_H
 #define NVIM_OS_UNIX_DEFS_H
 
-// Windows doesn't have unistd.h, so we include it here to avoid numerous
-// instances of `#ifdef WIN32'.
+// Windows doesn't have the following headers,
+// so we include them here to avoid numerous instances of `#ifdef WIN32'.
 #include <unistd.h>
+#include <sys/param.h>
 
 // POSIX.1-2008 says that NAME_MAX should be in here
 #include <limits.h>