[OPENMP] Drop type qualifiers from private variables.

[OPENMP] Drop type qualifiers from private variables.

If the variable is marked as private in OpenMP construct, the reference to this variable should not keep type qualifiers for the original variable. Private copy is not volatile or constant, so we can use unqualified type for private copy.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@242133 91177308-0d34-0410-b5e6-96231b3b80d8