prebirth: Ignore comments in JS parser

* build-aux/bootstrap/prebirth.js (parseLisp): Ingore comment tokens.
  (_lex): Recognize comments.

build-aux/bootstrap/prebirth.js

@@ -97,6 +97,10 @@ class Parser
             // a very simple bootstrap lisp)
             switch ( type )
             {
+                // ignore comments
+                case 'comment':
+                   return result;
+
                 // closing parenthesis (end of sexp)
                 case 'close':
                     if ( depth === 0 ) {
@@ -197,6 +201,12 @@ class Parser
             return [];
         }
 
+        // comment until end of line
+        if ( trim[ 0 ] === ';' ) {
+            const eol = trim.match( /^(.*?)(\n|$)/ );
+            return this._token( 'comment', eol[ 1 ], trim, pos );
+        }
+
         // left and right parenthesis are handled in the same manner: they
         // produce distinct tokens with single-character lexemes
         if ( trim[ 0 ] === '(' ) {