[OPENMP]Fix handling of the LCVs in loop-based directives.

[OPENMP]Fix handling of the LCVs in loop-based directives.

Loop-control variables with the default data-sharing attributes should
not be captured in the OpenMP region as they are private by default.
Also, default attributes should be emitted for such variables in the
inner OpenMP regions for the correct data sharing during codegen.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347409 91177308-0d34-0410-b5e6-96231b3b80d8