patch 8.0.0163: cannot build with Ruby 2.4

Problem:    Ruby 2.4 no longer supports rb_cFixnum.
Solution:   move rb_cFixnum into an #ifdef. (Kazuki Sakamoto, closes #1365)

Author: brammool

src/if_ruby.c

@@ -514,9 +514,10 @@ static struct
 {
     {"rb_assoc_new", (RUBY_PROC*)&dll_rb_assoc_new},
     {"rb_cFalseClass", (RUBY_PROC*)&dll_rb_cFalseClass},
-    {"rb_cFixnum", (RUBY_PROC*)&dll_rb_cFixnum},
 # if defined(USE_RUBY_INTEGER)
     {"rb_cInteger", (RUBY_PROC*)&dll_rb_cInteger},
+# else
+    {"rb_cFixnum", (RUBY_PROC*)&dll_rb_cFixnum},
 # endif
 # if defined(DYNAMIC_RUBY_VER) && DYNAMIC_RUBY_VER >= 20
     {"rb_cFloat", (RUBY_PROC*)&dll_rb_cFloat},

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    163,
 /**/
     162,
 /**/