x86: Don't use POSIX character classes in gen-insn-attr-x86.awk

Not all awk implementations (including the default awk in Ubuntu 9.10)
support POSIX character classes.  Since x86-opcode-map.txt is plain
ASCII, we can just use explicit ranges for lower case, alphabetic, and
alphanumeric characters instead.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
LKML-Reference: <adabphy750b.fsf@roland-alpha.cisco.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>