[Flang][OpenMP] wrong result with BLOCK in target region

[ye-luo]

I tested AMD downstream compiler and realized that the issue was from upstream.
flang version 20.0.0git (https://github.com/llvm/llvm-project.git 5a5502b)

Got wrong results regardless of enabling offload or not.

Code https://github.com/ye-luo/openmp-target/blob/master/tests/private/target_local_block.f90

yeluo@epyc-server:~/opt/openmp-target/tests/private$ flang -fopenmp --offload-arch=gfx906 target_local_block.f90 && ./a.out
flang-20: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
flang-20: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
flang-20: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 collect_a expected 20, now =  10
Fortran STOP: code 1

IEEE arithmetic exceptions signaled: INEXACT
yeluo@epyc-server:~/opt/openmp-target/tests/private$ flang -fopenmp target_local_block.f90 && ./a.out
flang-20: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 collect_a expected 20, now =  10
Fortran STOP: code 1