Previously, loop constructs were parsed in a piece-wise manner: the
begin directive, the body, and the end directive were parsed separately.
Later on in canonicalization they were all coalesced into a loop
construct. To facilitate that end-loop directives were given a special
treatment, namely they were parsed as OpenMP constructs. As a result
syntax errors caused by misplaced end-loop directives were handled
differently from those cause by misplaced non-loop end directives.

The new loop nest parser constructs the complete loop construct,
removing the need for the canonicalization step. Additionally, it is the
basis for parsing loop-sequence-associated constructs in the future.

It also removes the need for the special treatment of end-loop
directives. While this patch temporarily degrades the error messaging
for misplaced end-loop directives, it enables uniform handling of any
misplaced end-directives in the future.

This patch adds semantics for the `omp fuse` directive in flang, as
specified in OpenMP 6.0. This patch also enables semantic support for
loop sequences which are needed for the fuse directive along with
semantics for the `looprange` clause. These changes are only semantic.
Relevant tests have been added , and previous behavior is retained with
no changes.

---------

Co-authored-by: Ferran Toda <ferran.todacasaban@bsc.es>
Co-authored-by: Krzysztof Parzyszek <Krzysztof.Parzyszek@amd.com>

Replace use of flang -fc1 with %flang_fc1 in few test case

When a derived type has the same name as a generic function, and is
use-associated into a scope along with other distinct derived types of
the same name, we crash. Don't crash.

Fixes https://github.com/llvm/llvm-project/issues/168099.

This PR fixes a Fortran syntax violation in the OpenMP default mapper
naming convention. The suffix .omp.default.mapper contains dots which
are invalid in Fortran identifiers, causing failures when mappers are
written to and read from module files. The fix changes the suffix to
_omp_default_mapper which uses underscores instead of dots, complying
with Fortran syntax rules.

Key changes:

- Changed OmpDefaultMapperName constant from .omp.default.mapper to
_omp_default_mapper
- Added GetUltimate() calls in mapper symbol resolution to properly
handle symbols across module boundaries
- Added new test case verifying default mappers work correctly when
defined in a module and used in consuming programs

This fixes #168336.

Instead of storing a variant with specific types, store parser::Block as
the body. Add two access functions to make the traversal of the nest
simpler.

This will allow storing loop-nest sequences in the future.

Currently we're picking up and complaining about builtin (and procedure)
symbols like null() when defaultmap(none) is set, so I've relaxed the
restriction a bit to allow for procedures and named constants to bypass
the restriction. It might be the case that we want to tighten it up
again in certain aspects in the future.

There are a few well-meaning warnings for some cases of the FPTR=
argument to C_F_POINTER() that can be false positives, since the
restrictions in the standard are dependent on the source of the CPTR=
argument. Further, there is no way to alter a program to avoid these
warnings, so one cannot compile a correct and conforming program with
-pedantic -Werror. Disable these warnings.

Fixes https://github.com/llvm/llvm-project/issues/167470.