[OPENMP]Mark the loop as started when initialized.

[OPENMP]Mark the loop as started when initialized.

Need to mark the loop as started when the initialization statement is
found. It is required to prevent possible incorrect loop iteraton
variable detection during template instantiation and fix the compiler
crash during the codegen.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@349657 91177308-0d34-0410-b5e6-96231b3b80d8