[OpenMP] Update the default version of OpenMP to 5.1

The default version of OpenMP is updated from 5.0 to 5.1 which means if -fopenmp is specified but -fopenmp-version is not specified with clang, t

[OpenMP] Update the default version of OpenMP to 5.1

The default version of OpenMP is updated from 5.0 to 5.1 which means if -fopenmp is specified but -fopenmp-version is not specified with clang, the default version of OpenMP is taken to be 5.1. After modifying the Frontend for that, various LIT tests were updated. This patch contains all such changes. At a high level, these are the patterns of changes observed in LIT tests -

# RUN lines which mentioned `-fopenmp-version=50` need to kept only if the IR for version 5.0 and 5.1 are different. Otherwise only one RUN line with no version info(i.e. default version) needs to be there.

# Test cases of this sort already had the RUN lines with respect to the older default version 5.0 and the version 5.1. Only swapping the version specification flag `-fopenmp-version` from newer version RUN line to older version RUN line is required.

# Diagnostics: Remove the 5.0 version specific RUN lines if there was no difference in the Diagnostics messages with respect to the default 5.1.

# Diagnostics: In case there was any difference in diagnostics messages between 5.0 and 5.1, mention version specific messages in tests.

# If the test contained version specific ifdef's e.g. "#ifdef OMP5" but there were no RUN lines for any other version than 5.X, then bring the code guarded by ifdef's outside and remove the ifdef's.

# Some tests had RUN lines for both 5.0 and 5.1 versions, but it is found that the IR for 5.0 is not different from the 5.1, therefore such RUN lines are redundant. So, such duplicated lines are removed.

# To generate CHECK lines automatically, use the script llvm/utils/update_cc_test_checks.py

Reviewed By: saiislam, ABataev

Differential Revision: https://reviews.llvm.org/D129635

(cherry picked from commit 9dd2999907dc791136a75238a6000f69bf67cf4e)

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[Clang][OpenMP] Allow loop-transformations with template parameters.

Clang would reject

#pragma omp for
#pragma omp tile sizes(P)
for (int i = 0; i < 128; ++i) {}

where P is a template

[Clang][OpenMP] Allow loop-transformations with template parameters.

Clang would reject

#pragma omp for
#pragma omp tile sizes(P)
for (int i = 0; i < 128; ++i) {}

where P is a template parameter, but the loop itself is not
template-dependent. Because P context-dependent, the TransformedStmt
cannot be generated and therefore is nullptr (until the template is
instantiated by TreeTransform). The OMPForDirective would still expect
the a loop is the dependent context and trigger an error.

Fix by introducing a NumGeneratedLoops field to OMPLoopTransformation.
This is used to distinguish the case where no TransformedStmt will be
generated at all (e.g. #pragma omp unroll full) and template
instantiation is needed. In the latter case, delay resolving the
iteration space like when the for-loop itself is template-dependent
until the template instatiation.

A more radical solution would always delay the iteration space analysis
until template instantiation, but would also break many test cases.

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D111124

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[OpenMP] Implement '#pragma omp unroll'.

Implementation of the unroll directive introduced in OpenMP 5.1. Follows the approach from D76342 for the tile directive (i.e. AST-based, not using the OpenM

[OpenMP] Implement '#pragma omp unroll'.

Implementation of the unroll directive introduced in OpenMP 5.1. Follows the approach from D76342 for the tile directive (i.e. AST-based, not using the OpenMPIRBuilder). Tries to use `llvm.loop.unroll.*` metadata where possible, but has to fall back to an AST representation of the outer loop if the partially unrolled generated loop is associated with another directive (because it needs to compute the number of iterations).

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D99459

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