Given "loop" construct, clang will try to treat it as "for",
"distribute" or "simd", depending on either the implied binding, or the
bind clause if present. This patch moves the code that performs this
construct remapping from sema to codegen.

For a "loop" construct without a bind clause, this patch will create an
implicit bind clause based on implied binding to simplify further
analysis.

During codegen the function `EmitOMPGenericLoopDirective` (i.e. "loop")
will invoke the "emit" functions for "for", "distribute" or "simd",
depending on the bind clause.

---------

Co-authored-by: Alexey Bataev <a.bataev@gmx.com>

Just re-running the script to make future updates easier

Support for Code Generation of "#pragma loop bind" clause.
1) bind(parallel)
2) bind(teams)
3) bind(thread)

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D144634

This reverts commit 8e7f0320ad7fb760fff598aba4b2c86528c58c2d.
As requested on https://reviews.llvm.org/rG8e7f0320ad7fb760f#1236457

This reverts commit 4097a24584121dba562d471fab97d3dfec1b5bff.
Breaks tests on macOS, see https://reviews.llvm.org/rG4097a2458412#1235854

The loop directive is a descriptive construct which allows the compiler
flexibility in how it generates code for the directive's associated
loop(s). See OpenMP specification 5.2 [257:8-9].

Codegen added in this patch for the combined 'loop' directives are:

'target teams loop'     -> 'target teams distribute parallel for'
'teams loop'            -> 'teams distribute parallel for'
'target parallel loop'  -> 'target parallel for'
'parallel loop'         -> 'parallel for'

NOTE: The implementation of the 'loop' directive itself is unchanged.

Differential Revision: https://reviews.llvm.org/D145823