1. constants can never occur in the symbol table.

1. constants can never occur in the symbol table.
2. All function-level constants are now incorporated into the module-level
  constant pool, since the compaction table was removed.  Eliminate extra
  work to check for them.

This speeds up the bcwriter from 24.4s to 13.1s on 447.dealII and .73 -> .56s
on kc++ in a release build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34084 91177308-0d34-0410-b5e6-96231b3b80d8