Change the syntax for parameter attributes:

1. The @ sign is no longer necessary.
2. We now support "function attributes" as parameter attribute 0.
3. Instead of locating the return type attributes after the type of a
   function result, they are now located after the function header's
   closing paranthesis and before any alignment or section options.
4. The way has been prepared for a new "noreturn" function attribute but
   there is no support for recognizing it in the lexer nor doing anything
   with it if it does get set.
5. The FunctionType::getParamAttrsText method now has support for
   returning multiple attributes. This required a change in its interface.

I'm unhappy that this change leads to 6 new shift/reduce conflicts, but
in each case bison's decision to choose the shift is correct so there
shouldn't be any damage from these conflicts.

llvm-svn: 32904