add a new -fdiagnostics-show-category=none/id/name option, giving control

add a new -fdiagnostics-show-category=none/id/name option, giving control
over choice of:

t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat,1]
t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat,Format String]

dox to come.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@103056 91177308-0d34-0410-b5e6-96231b3b80d8