Didn't find a test for this (but there are tests for the `Function`
version of this pass)

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.

Emit all constant integers produced by SanitizerBinaryMetadata as
ULEB128 to further reduce binary space used. Increasing the version is
not necessary given this change depends on (and will land) along with
the bump to v2.

To support this, the !pcsections metadata format is extended to allow
for per-section options, encoded in the first MD operator which must
always be a string and contain the section: "<section>!<options>".

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D143484

Optimize the encoding of "covered" metadata by:

 1. Reducing feature mask from 4 bytes to 1 byte (needs increase once we
    reach more than 8 features).

 2. Only emitting UAR stack args size if it is non-zero, saving 4 bytes
    in the common case.

One caveat is that the emitted metadata for function PC (offset), size,
and UAR size (if enabled) are no longer aligned to 4 bytes.

SanitizerBinaryMetadata version base is increased to 2, since the change
is backwards incompatible.

Reviewed By: dvyukov

Differential Revision: https://reviews.llvm.org/D143482

Currently per-function metadata consists of:
(start-pc, size, features)

This adds a new UAR feature and if it's set an additional element:
(start-pc, size, features, stack-args-size)

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D136078

This reverts commit d3c851d3fc8b69dda70bf5f999c5b39dc314dd73.

Some bots broke:

- https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-linux-x64/b8796062278266465473/overview
- https://lab.llvm.org/buildbot/#/builders/124/builds/5759/steps/7/logs/stdio

Currently per-function metadata consists of:
(start-pc, size, features)

This adds a new UAR feature and if it's set an additional element:
(start-pc, size, features, stack-args-size)

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D136078

This reverts commit e6aea4a5db09c845276ece92737a6aac97794100.

Broke tests:
https://lab.llvm.org/buildbot/#/builders/16/builds/38992

Currently per-function metadata consists of:
(start-pc, size, features)

This adds a new UAR feature and if it's set an additional element:
(start-pc, size, features, stack-args-size)

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D136078