[clang] [flang] [llvm] seq_cst is allowed in Flush since OpenMP 5.1. (PR #114072)

[Kiran Chandramohan via cfe-commits]

https://github.com/kiranchandramohan approved this pull request.

LG. Please add the test I suggested. Please wait for @alexey-bataev 

https://github.com/llvm/llvm-project/pull/114072