Align symbol table columns in the generated C code

At the end of the VGC we output the contents of the symbol table inside
a C comment. It might look like this:

    /*
     * Symbol Table
     *
     * reserved  VOID       41 41 acl
     * reserved  VOID       41 41 backend
     * action    VOID       40 41 ban
     * var       HTTP        0 99 bereq
     * var       BACKEND     0 99 bereq.backend
     * [...]
     */

All columns are currently aligned because we know all the native VCL
types and only the last column with the symbol names has unpredictable
and arbitrary entries lengths.

However, considering the following snippet:

    new fb = directors.fallback();

The involved symbols will look like:

    object    VOID      41 41 directors.fallback
    instance  INSTANCE  41 41 fb
    func      VOID      40 41 fb.add_backend
    func      BACKEND   40 41 fb.backend
    func      VOID      40 41 fb.remove_backend

In the future VMOD objects will likely grow their own types and for the
same snippet we may have this instead:

    object    directors.fallback  41 41 directors.fallback
    method    VOID                40 41 directors.fallback.add_backend
    method    BACKEND             40 41 directors.fallback.backend
    method    VOID                40 41 directors.fallback.remove_backend
    instance  directors.fallback  41 41 fb

This change was initially submitted as part of #3147, but was considered
trivial and fast-track-able by PHK.

lib/libvcc/vcc_xref.c

@@ -322,6 +322,21 @@ vcc_CheckUses(struct vcc *tl)
 
 /*---------------------------------------------------------------------*/
 
+static int sym_type_len = 0;
+
+static void v_matchproto_(symwalk_f)
+vcc_xreftable_len(struct vcc *tl, const struct symbol *sym)
+{
+	int len;
+
+	(void)tl;
+	CHECK_OBJ_NOTNULL(sym, SYMBOL_MAGIC);
+	CHECK_OBJ_NOTNULL(sym->type, TYPE_MAGIC);
+	len = strlen(sym->type->name);
+	if (sym_type_len < len)
+		sym_type_len = len;
+}
+
 static void v_matchproto_(symwalk_f)
 vcc_xreftable(struct vcc *tl, const struct symbol *sym)
 {
@@ -330,7 +345,7 @@ vcc_xreftable(struct vcc *tl, const struct symbol *sym)
 	CHECK_OBJ_NOTNULL(sym->kind, KIND_MAGIC);
 	CHECK_OBJ_NOTNULL(sym->type, TYPE_MAGIC);
 	Fc(tl, 0, " * %-8s ", sym->kind->name);
-	Fc(tl, 0, " %-9s ", sym->type->name);
+	Fc(tl, 0, " %-*s ", sym_type_len, sym->type->name);
 	Fc(tl, 0, " %2u %2u ", sym->lorev, sym->hirev);
 	VCC_SymName(tl->fc, sym);
 	if (sym->wildcard != NULL)
@@ -343,6 +358,7 @@ VCC_XrefTable(struct vcc *tl)
 {
 
 	Fc(tl, 0, "\n/*\n * Symbol Table\n *\n");
+	VCC_WalkSymbols(tl, vcc_xreftable_len, SYM_NONE);
 	VCC_WalkSymbols(tl, vcc_xreftable, SYM_NONE);
 	Fc(tl, 0, "*/\n\n");
 }