Convert collapseBlocks functions in to methods on FnSymbol and BlockStmt
Update the interface to buildVarDecls for LLVM
Merge pull request #767 from noakesmichael/collapseBlocks

Initial code shuffle collapse blocks and fix for LLVM

1) There is an operation that collapses nested BlockStmts in appropriate contexts.  The current implementation must be refactored as part of the While/For loop refactoring.  This is an initial trivial code shuffle to convert 
existing function in to AST class methods.  No change in functionality.

2) Also an update to LLVM code to conform to the new interface to buildVarDecls.


Compiled: Clang darwin STD, GCC linux64 STD, GCC linux64 LLVM
Tested: Full regression suite STD and LLVM
Reviewed: None