- Remove unused STRING token from lexer & parser

 - Remove unused STRING token from lexer & parser
  - Changed parser to always use parenthesis on ConstExprs to be consistent
  - Parser now passes TRUE and FALSE tokens as a special case of the ConstExpr
    machinery instead of a special case of constant int stuff
  - Fix the AsmParser to use ValueRef ::= ConstExpr, and remove
    ResolvedVal ::= ConstExpr this allows constexprs to be used in PHI nodes

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3362 91177308-0d34-0410-b5e6-96231b3b80d8