Earlier creation of ScopStmt objects

This moves the construction of ScopStmt to the beginning of the 
ScopInfo pass. The late creation was a result of the earlier separation 
of ScopInfo and TempScopInfo. This will avoid introducing more 
ScopStmt-like maps in future commits. The AccFuncMap will also be 
removed in some future commit. DomainMap might also be included into 
ScopStmt.

The order in which ScopStmt are created changes and initially creates 
empty statements that are removed in a simplification.

Differential Revision: http://reviews.llvm.org/D13341

llvm-svn: 249132