add and document regex support for FileCheck.  You can now do stuff like:
add and document regex support for FileCheck.  You can now do stuff like:

; CHECK: movl {{%e[a-z][xi]}}, %eax

or whatever.



git-svn-id: a4a6f32337ebd29ad4763b423022f00f68d1c7b7@82717 91177308-0d34-0410-b5e6-96231b3b80d8

lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx,lodyagin/bare_cxx