This commit implements the entirety of the now-accepted [N3017
-Preprocessor
Embed](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm) and
its sister C++ paper [p1967](https://wg21.link/p1967). It implements
everything in the specification, and includes an implementation that
drastically improves the time it takes to embed data in specific
scenarios (the initialization of character type arrays). The mechanisms
used to do this are used under the "as-if" rule, and in general when the
system cannot detect it is initializing an array object in a variable
declaration, will generate EmbedExpr AST node which will be expanded by
AST consumers (CodeGen or constant expression evaluators) or expand
embed directive as a comma expression.

This reverts commit
https://github.com/llvm/llvm-project/commit/682d461d5a231cee54d65910e6341769419a67d7.

---------

Co-authored-by: The Phantom Derpstorm <phdofthehouse@gmail.com>
Co-authored-by: Aaron Ballman <aaron@aaronballman.com>
Co-authored-by: cor3ntin <corentinjabot@gmail.com>
Co-authored-by: H. Vetinari <h.vetinari@gmx.com>

Reverts llvm/llvm-project#68620

Introduce or expose a memory leak and UB, see llvm/llvm-project#68620

This commit implements the entirety of the now-accepted [N3017 -
Preprocessor
Embed](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm) and
its sister C++ paper [p1967](https://wg21.link/p1967). It implements
everything in the specification, and includes an implementation that
drastically improves the time it takes to embed data in specific
scenarios (the initialization of character type arrays). The mechanisms
used to do this are used under the "as-if" rule, and in general when the
system cannot detect it is initializing an array object in a variable
declaration, will generate EmbedExpr AST node which will be expanded
by AST consumers (CodeGen or constant expression evaluators) or
expand embed directive as a comma expression.

---------

Co-authored-by: Aaron Ballman <aaron@aaronballman.com>
Co-authored-by: cor3ntin <corentinjabot@gmail.com>
Co-authored-by: H. Vetinari <h.vetinari@gmx.com>
Co-authored-by: Podchishchaeva, Mariya <mariya.podchishchaeva@intel.com>

These three clauses are all quite trivial, as they take no parameters.
They are mutually exclusive, and 'seq' has some other exclusives that
are implemented here.

The ONE thing that isn't implemented is 2.9's restriction (line 2010):
  'A loop associated with a 'loop' construct that does not have a 'seq'
   clause must be written to meet all the following conditions'.

Future clauses will require similar work, so it'll be done as a
followup.

This patch implements the 'loop' construct AST, as well as the basic
appertainment rule. Additionally, it sets up the 'parent' compute
construct, which is necessary for codegen/other diagnostics.

A 'loop' can apply to a for or range-for loop, otherwise it has no other
restrictions (though some of its clauses do).

'reduction' has a few restrictions over normal 'var-list' clauses:

1- On parallel, a num_gangs can only have 1 argument when combined with
reduction. These two aren't able to be combined on any other of the
compute constructs however.

2- The vars all must be 'numerical data types' types of some sort, or a
'composite of numerical data types'. A list of types is given in the
standard as a minimum, so we choose 'isScalar', which covers all of
these types and keeps types that are actually numeric. Other compilers
don't seem to implement the 'composite of numerical data types', though
we do.

3- Because of the above restrictions, member-of-composite is not
allowed, so any access via a memberexpr is disallowed. Array-element and
sub-arrays (aka array sections) are both permitted, so long as they meet
the requirements of #2.

This patch implements all of these for compute constructs.

device_type, also spelled as dtype, specifies the applicability of the
clauses following it, and takes a series of identifiers representing the
architectures it applies to.  As we don't have a source for the valid
architectures yet, this patch just accepts all.

Semantically, this also limits the list of clauses that can be applied
after the device_type, so this implements that as well.

This reverts commit 06f04b2e27f2586d3db2204ed4e54f8b78fea74e.
This reapplies commit c4a9a374749deb5f2a932a7d4ef9321be1b2ae5d.
The build failures were caused by the patch depending on the order of
evaluation of arguments to a function. This reapplication separates out
the capture of one of the values.

This reverts commit c4a9a374749deb5f2a932a7d4ef9321be1b2ae5d.

This and the followup patch keep hitting an assert I wrote on the build
bots in a way that isn't clear.  Reverting so I can fix it without a
rush.

device_type, also spelled as dtype, specifies the applicability of the
clauses following it, and takes a series of identifiers representing the
architectures it applies to.  As we don't have a source for the valid
architectures yet, this patch just accepts all.

Semantically, this also limits the list of clauses that can be applied
after the device_type, so this implements that as well.

'wait' takes a few int-exprs (well, a series of async-arguments, but
    those are effectively just an int-expr), plus a pair of tags. This
patch adds the support for this to the AST, and does the appropriate
semantic analysis for them.