This patch implements the following check for TEAMS construct:
```
OpenMP Version 5.0 Teams construct restriction: A teams region can
only be strictly nested within the implicit parallel region or a target
region. If a teams construct is nested within a target construct, that
target construct must contain no statements, declarations or directives
outside of the teams construct.
```
Also add one test case for the check.
Reviewed By: kiranchandramohan, clementval
Differential Revision: https://reviews.llvm.org/D106335
Allow the lit test suite to run under Windows. This encompasses the following changes:
* Define `lit_tools_dir` for flang's test configuration
* Replace `(<command> || true)` idiom with `not <command>`
* Add `REQUIRES: shell` on tests that invoke a shell script
Reviewed By: awarzynski
Differential Revision: https://reviews.llvm.org/D89368
Peixin Qiao