This was missed in 0ef522ff68fff4266bf85e7b7a507a16a8fd34ee

This improves type safety and is less verbose. Use SimpleTy only where
an integer is needed like switches or emitting a VBR.

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Co-authored-by: Sergei Barannikov <barannikov88@gmail.com>

Identified with bugprone-unused-local-non-trivial-variable.

OpenMP 6.0 introduced a `fuse` directive, and with it a "loop sequence"
as the associated code. What used to be "loop association" has become
"loop-nest association".

Rename Association::Loop to LoopNest, add Association::LoopSeq to
represent the "loop sequence" association.

Change the association of fuse from "block" to "loop sequence".

Use `IfGuardEmitter` in CallingConvEmitter. Additionally refactor the
code a bit to extract duplicated code to emit the CC function prototype
into a helper function.

The collection of library function names in TargetLibraryInfo faces
similar challenges as RuntimeLibCalls in the IR component. The number of
function names is large, there are numerous customizations based on the
triple (including alternate names), and there is a lot of replicated
data in the signature table.

The ultimate goal would be to capture all lbrary function related
information in a .td file. This PR brings the current .def file to
TableGen, almost as a 1:1 replacement. However, there are some
improvements which are not possible in the current implementation:

- the function names are now stored as a long string together with an
offset table.
- the table of signatures is now deduplicated, using an offset table for
access.

The size of the object file decreases about 34kB with these changes. The
hash table of all function names is still constructed dynamically. A
static table like for RuntimeLibCalls is the next logical step.

The main motivation for this change is that I have to add a large number
of custom names for z/OS (like in RuntimeLibCalls.td), and the current
infrastructur does not support this very well.

This patch changes the type of SubRegIndicesSize to size_t.  The
original type deduced for "auto" is a signed type, but size_t, an
unsigned type, is safe here according to the usage.

Add a RAII `IfGuardEmitter` to insert simple #if guards and adopt it in
InstrInfoEmitter.

Note that llvm::size only works on types that allow std::distance in
O(1).