prebirth: Distinguishable id generation

* build-aux/bootstrap/prebirth.js (Compiler#_idFromName): Distinguish
  between certain types of characters.

build-aux/bootstrap/prebirth.js

@@ -375,6 +375,12 @@ class Compiler
     /**
      * Generate ECMAScript-friendly name from the given id
      *
+     * A subset of special characters that are acceptable in Scheme are
+     * converted in an identifiable manner; others are simply converted to
+     * `$' in a catch-all and therefore could result in conflicts and cannot
+     * be reliably distinguished from one-another.  Remember: this is
+     * temporary code.
+     *
      * @param {string}  name   source name
      * @param {boolean} global whether identifier should be globally unique
      *
@@ -382,8 +388,31 @@ class Compiler
      */
     _idFromName( name, global )
     {
-        return ( global ? '$$' : '' )
-            + name.replace( /[^a-zA-Z0-9_]/g, '$' );
+        // just some common ones; will fall back to `$' below
+        const conv = {
+            '-': '$_$',
+            '?': '$7$',
+            '@': '$a$',
+            '!': '$b$',
+            '>': '$g$',
+            '#': '$h$',
+            '*': '$k$',
+            '<': '$l$',
+            '&': '$n$',
+            '%': '$o$',
+            '+': '$p$',
+            '=': '$q$',
+            '^': '$v$',
+            '/': '$w$',
+            '$': '$$',
+        };
+
+        if ( name === undefined ) {
+            throw SyntaxError( "Missing identifier name" );
+        }
+
+        return ( global ? '$$' : '' ) +
+            name.replace( /[^a-zA-Z0-9_]/g, c => conv[ c ] || '$' );
     }