wcc/cgen: drop underscore from cgen_*.ww filenames

selfhost/cmd/wcc/cgen.ww

@@ -31,11 +31,11 @@ use sym;
 use strconv;
 // Split files. Bundler pulls these in transitively so consumers only
 // need `use cgen;`. Order matters for the flat-bundle concat — utils
-// first so cgen_expr/stmt/decl can reference helpers defined here.
-use cgen_util;
-use cgen_expr;
-use cgen_stmt;
-use cgen_decl;
+// first so cgenexpr/stmt/decl can reference helpers defined here.
+use cgenutil;
+use cgenexpr;
+use cgenstmt;
+use cgendecl;
 
 // ---- typedef alias registry -----------------------------------------
 //