This change was mistakenly dropped from the prior commit 6b623a6622707ea47d84ab0069f766215a6fec44

Version 2 was added more than two years ago
(https://github.com/llvm/llvm-project/commit/6015a045d768feab3bae9ad9c0c81e118df8b04a).
So it should be safe to deprecate older versions.

Work towards separating the ABI existence of libcalls vs. the
lowering selection. Set libcall selection through enums, rather
than through raw string names.

Replace RuntimeLibcalls.def with a tablegenerated version. This
is in preparation for splitting RuntimeLibcalls into two components.
For now match the existing functionality.

ArrayRef now has a new constructor that takes a parameter whose type
has data() and size().  This patch migrates:

  ArrayRef<T>(X.data(), X.size()

to:

  ArrayRef<T>(X)

Recently, we have been looking at some optimizations targeting
individual calls. In particular, we plan to extend the address mapping
technique to map to individual callsites. For example, in this piece of
code for a basic blocks:

```
<BB>:
1200:    lea 0x1(%rcx), %rdx
1204:    callq foo
1209:    cmpq 0x10, %rdx
120d:    ja  L1
```

We want to emit 0x9 as the call site offset for `callq foo` (the offset
from the block entry to right after the call), so that we know if a
sampled address is before the call or after.

This PR implements the decode/encode/emit capability. The Codegen change
will be implemented in a later PR.

This is just a stub for now.

We need the full set of ABI options to accurately compute
the full set of libcalls. This partially resolves missing
information required to compute the set of ARM calls.