Identified with misc-include-cleaner.

Avoid excess layer of indirection.

In ARM mode, the Program Counter (PC) points to the current instruction's
address + 8 instead of + 4. An offset is added to RuntimeDyldChecker to
use `next_pc` expression in JITLink tests with both Thumb and Arm.

We use `jitlink-check` lines in LIT tests as the primary tool for
testing JITLink backends. Parsing and evaluation of the expressions is
implemented in `RuntimeDyldChecker`. The `stub_addr(obj, name)`
expression allows to obtain the linker-generated stub for the external
symbol `name` in object file `obj`.

This patch adds support for a filter parameter to select one out of many
stubs. This is necessary for the AArch32 JITLink backend, which must be
able to emit two different kinds of stubs depending on the instruction
set state (Arm/Thumb) of the relocation site. Since the new parameter is
optional, we don't have to update existing tests.

Filters are regular expressions without brackets that match exactly one
existing stub. Given object file `armv7.o` with two stubs for external
function `ext` of kinds `armv7_abs_le` and `thumbv7_abs_le`, we get the
following filter results e.g.:
```
stub_addr(armv7.o, ext, thumb)        thumbv7_abs_le
stub_addr(armv7.o, ext, thumbv7)      thumbv7_abs_le
stub_addr(armv7.o, ext, armv7_abs_le) armv7_abs_le
stub_addr(armv7.o, ext, v7_.*_le)     Error: "ext" has 2 candidate stubs in file "armv7.o". Please refine stub-kind filter "v7_.*_le" for disambiguation (encountered kinds are "thumbv7_abs_le", "armv7_abs_le").
stub_addr(armv7.o, ext, v8)           Error: "ext" has 2 stubs in file "armv7.o", but none of them matches the stub-kind filter "v8" (all encountered kinds are "thumbv7_abs_le", "armv7_abs_le").
```

This patch replaces uses of StringRef::{starts,ends}with with
StringRef::{starts,ends}_with for consistency with
std::{string,string_view}::{starts,ends}_with in C++20.

I'm planning to deprecate and eventually remove
StringRef::{starts,ends}with.

Now that llvm::support::endianness has been renamed to
llvm::endianness, we can use the shorter form.  This patch replaces
support::endianness with llvm::endianness.

This re-applies 4b17c81d5a5, "[jitlink/rtdydl][checker] Add TargetFlag
dependent disassembler switching support", which was reverted in
4871a9ca546 due to bot failures.

The patch has been updated to add missing plumbing for Subtarget Features and
a CPU string, which should fix the failing tests.

https://reviews.llvm.org/D158280

This reverts commit 4b17c81d5a5d3e0f514026c2b7f9b623d901cc04.

Caused buildbot failures:
https://lab.llvm.org/buildbot/#/builders/230/builds/18341
https://lab.llvm.org/buildbot/#/builders/109/builds/73169
https://lab.llvm.org/buildbot/#/builders/67/builds/12597

Some targets such as AArch32 make use of TargetFlags to indicate ISA mode. Depending
on the TargetFlag, MCDisassembler and similar target specific objects should be
reinitialized with the correct Target Triple. Backends with similar needs can
easily extend this implementation for their usecase.

The drivers llvm-rtdyld and llvm-jitlink have their SymbolInfo's extended to take
TargetFlag into account. RuntimeDyldChecker can now create necessary TargetInfo
to reinitialize MCDisassembler and MCInstPrinter. The required triple is obtained
from the new getTripleFromTargetFlag function by checking the TargetFlag.

In addition, breaking changes for RuntimeDyld COFF Thumb tests are fixed by making
the backend emit a TargetFlag.

Reviewed By: lhames, sgraenitz

Differential Revision: https://reviews.llvm.org/D158280

Reviewed By: sgraenitz

Differential Revision: https://reviews.llvm.org/D157226