Add missing #elifdef, #elifndef directives to C/C++ highlights (#45672)

Release Notes:

- Add missing #elifdef, #elifndef directives to C/C++ highlights.

crates/languages/src/c/highlights.scm

@@ -29,6 +29,8 @@
 [
   "#define"
   "#elif"
+  "#elifdef"
+  "#elifndef"
   "#else"
   "#endif"
   "#if"

crates/languages/src/cpp/highlights.scm

@@ -168,6 +168,8 @@ type: (primitive_type) @type.builtin
 [
   "#define"
   "#elif"
+  "#elifdef"
+  "#elifndef"
   "#else"
   "#endif"
   "#if"