Changes

Ensure we do not expect additional linker args to be produced in targets with Swift-produced object files (#378)

If Swift produced an object in the linked libraries of a target, we allow it to generate additional linker
options, even if it did not run to compile any source files. However, we should not attempt to inject top-level
AST paths for debugging since no actual compile took place, and the paths won't exist at execution time. Use the
object file type when injecting Swift tool usage in these targets so that we don't take the unintended code path.

rdar://144729550

[build-script-helper] Remove unneeded flags for Android

Removing the definition of `_GNU_SOURCE` is no longer needed since
swiftlang/swift-tools-support-core#500 made sure the right `strerror_r()` is used.

Bootstrap: update logic to support pre-and post python 3.8 (#8446)

PR #8373 (commit ID: 0193d5fb8) updated a `shutil.copytree(...)` command
to pass in the `dirs_exists_ok=True` argument. However, Python added
support for the `dirs_exists_ok` argument to `shutil.copytree` in 3.8.

Update the function call to inspect the python version, and only add the
argument if the script is running in a Python version equal, or higher
than 3.8.

rdar://147297864

Add a build flavor to opt-out of BTCFI on OpenBSD.

To work-around #80059, we need to stop return address signing and
opt-out of BTCFI enforcement via enabling a platform linker option.

We don't want to completely undo the BTCFI work in the rare case that
we later figure out how to properly address the above issue, or allow
users who might want to benefit from BTCFI enforcement and won't use
Concurrency. To do this, condition the existing BTCFI flag enforcement
into a configuration option that defaults to off for now.

Because the new swift-driver needs to "know" whether the frontend is
configured to opt-out or not, and since the new driver communicates with
the frontend via the target info JSON to begin with, we add a field
that emits the build flavor to signal the right behavior.

Revert "Concurrency: remove workaround for silencing UB"

[DebugInfo] Use underlying type of global variables with opaque type

rdar://144881938

[AST] Introduce `Expr::isAlwaysLeftFolded`

Use this to query for `try`-like expressions when it comes to binary
operator folding.

[ASTScope] Allow `try` in unfolded sequence to cover following elements

Rather than fixing-up in the parser, adjust the ASTScope logic such
that a `try` element in a SequenceExpr is considered as covering all
elements to the right of it. Cases where this isn't true are invalid,
and will be diagnosed during sequence folding. e.g:

```
0 * try foo() + bar()
_ = try foo() ~~~ bar() // Assuming `~~~` has lower precedence than `=`
```

This ensures we correctly handle `try` in assignment sequences, and
allows ASTGen to get the behavior for free.

rdar://132872235

SILCombine: fix an ownership violation when replacing open existential apply arguments

The value of the opened existential must outlive the apply. Otherwise the optimization creates invalid SIL.

rdar://148259849

SILCombine: fix a wrong assert in the SingleBlockOwnedForwardingInstFolder

[ExplicitModuleBuild] Don't leak chained bridging header in objc header

When generating an objc header from the swift module when a bridging
header is used, make sure to use the original bridging header, not
the chained bridging header. This also avoids incorrectly generated a
header include when no actual bridging header is used, just a chained
bridging header that is coming from a dependency.

rdar://148446465

MoveOnlyChecker: Don't follow trivial transitive uses of borrows.

Trivial values don't have ownership tracked, so their uses can't affect the
lifetime of the original borrow. Fixes rdar://148457155.

[Driver] Don't hardcode default linker on Linux

This is the C++ driver counterpart to a change that landed in the Swift
driver a while ago to use the clang-linker to determine what the default
linker is. This is to avoid hard-coding gold, which is deprecated and
not available on some newer Linux distributions. The challenge is that
these newer Linux distributions don't already have Swift so we have to
use the old C++ driver implementation.

stdlib: Address new #StrictMemorySafety warnings.

stdlib: Address unreachable code warnings.

[lldb] Add global opaque archetype test

rdar://144881938