Changes

[gn build] Build with Fission on non-mac non-win when using lld

In release+sym builds (-O2 -g), reduces time to link `clang`
from 2.3s to 1.3s (-42%).

In debug builds (-g), reduces time to link `clang`
from 5.4s to 4.5s (-17.4%).

See the phab review for full `ministat` numbers.

In the CMake build this is opt-in via LLVM_USE_SPLIT_DWARF.
Since the GN build is targeted at developers, enabling it by default
seems like a better default setting here. (If it turns out to cause
problems, we can add an opt-out.)

Time to load the binary into gdb and to set a breakpoint is unchanged.
Time from `run` to hitting a breakpoint in `main` feel a bit faster
(~4s -> ~2s), but I dind't do a careful statistical anlysis for this.

Differential Revision: https://reviews.llvm.org/D115040

[libc] Fix invalid include for SqrtLongDouble.h

[ARM] Replace if's with a switch, NFC

I'm not having a lot of luck with the microosft compiler recently. Maybe
this will help it with its errors:
llvm\lib\IR\AutoUpgrade.cpp(3726): fatal error C1061: compiler limit: blocks nested too deeply

If not, it's a good code cleanup anyway.

[ARM] Separate ARM autoupgrade code into a separate function

Try to appease the microsoft compiler which is apparently running out of
if statements. Separate the new ARM code into a separate function to
keep it simpler.

[LLDB] XFAIL on Arm/Linux minidebuginfo-set-and-hit-breakpoint.test

minidebuginfo-set-and-hit-breakpoint.test is failing on Arm/Linux most
probably due to an ill formed binary after removal of certain sections
from executable. I am marking it as XFAIL for further investigation.

[IR][AutoUpgrade] Merge x86 mask load intrinsic upgrades. NFC.

Helps appease MSVC which is complaining about "fatal error C1061: compiler limit: blocks nested too deeply" - we already do the same thing for avx512.mask.store intrinsics.

This is only a stopgap solution until another else-if case needs adding - we really need to refactor this chain of ifs properly.

[funcattrs] Fix a bug in recently introduced writeonly argument inference

This fixes a bug in 740057d.  There's two ways to describe the issue:
* One caller hasn't yet proven nocapture on the argument.  Given that, the inference routine is responsible for bailing out on a potential capture.
* Even if we know the argument is nocapture, the access inference needs to traverse the exact set of users the capture tracking would (or exit conservatively).  Even if capture tracking can prove a store is non-capturing (e.g. to a local alloc which doesn't escape), we still need to track the copy of the pointer to see if it's later reloaded and accessed again.

Note that all the test changes except the newly added ones appear to be false negatives.  That is, cases where we could prove writeonly, but the current code isn't strong enough.  That's why I didn't spot this originally.

[DAG] PromoteIntRes_FunnelShift - rename shift Amount variable to Amt to prevent line overflow. NFC.

[AMDGPU] Kill def when folding immediate in two-addr pass

Two-address pass works right before RA and if an immediate
was folded into an instruction there is nothing to remove
the dead def. We end up with something like:

	v_mov_b32_e32 v14, 0xc1700000
	v_mov_b32_e32 v14, 0x41200000
	v_fmaak_f32 v51, s67, v19, 0xc1700000
	v_fmaak_f32 v38, v51, v19, 0x4120000

The patch kills the dead move instruction right in the folding.

Differential Revision: https://reviews.llvm.org/D114999

[AMDGPU] Fixed incomplete definitions in twoaddr-fma.mir. NFC.

[HWASan] Try 'google' prefixed apex directories in symbolizer.

Google-signed apexes appear on Android build servers' symbol files as
being under /apex/com.google.android.<foo>/. In reality, the apexes are
always installed as /apex/com.android.<foo>/ (note the lack of
'google'). In order for local symbolization under hwasan_symbolize to
work correctly, we also try the 'google' directory.

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D114919

[CFG] Handle calls with funclet bundle

When Control Flow Guard Check is inserted, funclet bundle was not checked. Therefore, it didn't generate code correctly when a target function has "funclet" bundle.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D114914

[libunwind] Fix unwind_leaffunction test

It's possible for this test not to pass if the libc used does not provide
unwind info for raise. We can replace it with __builtin_cast, which can lead
to a SIGTRAP on x86_64 and a SIGILL on aarch64.

Using this alternative, a nop is needed before the __builtin_cast. This is
because libunwind incorrectly decrements pc, which can cause pc to jump into
the previous function and use the incorrect FDE.

Differential Revision: https://reviews.llvm.org/D114818

[msan] Don't block SIGSYS in ScopedBlockSignals

Seccomp-BPF-sandboxed processes rely on being able to process SIGSYS
signals.

Differential revision: https://reviews.llvm.org/D115057