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.

Since VD is assigned from a cast<VarDecl> it cannot be a nullptr or it
would have asserted. Remove the subsequent checks to clear up any
misunderstanding.

Currently target_clones attribute results in a linker error when there
are no multi-versioned function declarations in the calling TU.

In the calling TU, the call is generated with the ‘normal’ assembly
name. This does not match any of the versions or the ifunc, since
version mangling includes a .versionstring, and the ifunc includes
.ifunc suffix. The linker error is not seen with GCC since the mangling
for the ifunc symbol in GCC is the ‘normal’ assembly name for function
i.e. no ifunc suffix.

This PR removes the .ifunc suffix to match GCC. It also adds alias with
the .ifunc suffix so as to ensure backward compatibility.

The changes exclude aarch64 target because the mangling for default
versions on aarch64 does not include a .default suffix and is the
'normal' assembly name, unlike other targets. It is not clear to me what
the correct behavior for this target is.

Old Phabricator review - https://reviews.llvm.org/D158666

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Co-authored-by: Tom Honermann <tom@honermann.net>

Previously, annotations were only emitted for function definitions. With
this change annotations are also emitted for declarations. Also,
emitting function annotations is now deferred until the end so that the
most up to date declaration is used which will have any inherited
annotations.

Information about code object version can be configured by the user for
AMD GPU target and it needs to be placed in LLVM IR generated by Flang.

Information about code object version in MLIR generated by the parser
can be reused by other tools. There is no need to specify extra flags if
we want to invoke MLIR tools (like fir-opt) separately.

Changes in comparison to a8ac93:
 * added information about required targets for test
   flang/test/Driver/driver-help.f90

This commit causes test errors on buildbots.

This reverts commit a8ac930b99d93b2a539ada7e566993d148899144.

Information about code object version can be configured by the user for
AMD GPU target and it needs to be placed in LLVM IR generated by Flang.

Information about code object version in MLIR generated by the parser
can be reused by other tools. There is no need to specify extra flags if
we want to invoke MLIR tools (like fir-opt) separately.

This PR adds support for the PPA2 fields.

---------

Co-authored-by: Yusra Syeda <yusra.syeda@ibm.com>

Opaque ptr cleanup effort (NFC)