The attached patch fixes bug 11067 "p <enum constant> should print the 
constant's value" by providing a means of setting a format string to be 
used in printing enums.  The string is set with

    set enum-fmt <string>

show enum-fmt returns the current format string.

Here's the description from the relevant add_setshow_string_cmd()

    (gdb) help set enum-fmt
    Set enum display format.
    Allows a printf-style format string to be specified to control the
    display
    of enum values.  The string will be printed verbatim when enum
    values are
    displayed except that:
         %v directives will be expanded to the numeric value of the enum,
         %s directives will be expanded to the symbolic value of the
    enum, and
         %t directives will be expanded to the enum tag.
    The default format is equivalent to "%s" and the default will be used if
    no argument is provided to the set operation.
    (gdb)

This allows the user to print the value in any useful way.

    $1 = Val1
    $2 = Val1=(enum E)56
    $3 = Val2=(enum E)57
    $4 = Val1 = (enum E)56
    $5 = Val2 = (enum E)57
    $6 = 56 "Val1"
    $7 = 57 "Val2"

or whatever:

Patch attached, as is a diff of before-and-after gdb.sum