Apply clang fix for crash or assertion failure compiling part of llvm

Merge commit 77e8f4eeeeed from llvm git (by David Green):

[ARM] Define ComplexPatternFuncMutatesDAG

Some of the Arm complex pattern functions call canExtractShiftFromMul,
which can modify the DAG in-place. For this to be valid and handled
successfully we need to define ComplexPatternFuncMutatesDAG.

Differential Revision: https://reviews.llvm.org/D107476

When building parts of llvm targeting armv6 on stable/12, the following
assertion can appear (or if assertions are disabled, clang is likely to
crash):

Assertion failed: (NodeToMatch->getOpcode() != ISD::DELETED_NODE && "NodeToMatch was removed partway through selection"), function SelectCodeCommon, file /usr/src/contrib/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp, line 3573.
PLEASE submit a bug report to https://bugs.freebsd.org/submit/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: /usr/obj/usr/src/freebsd12-amd64/tmp/usr/bin/c++ -cc1 -triple armv6kz-unknown-freebsd12.3-gnueabihf -S --mrelax-relocations -disable-free -disable-llvm-verifier -discard-value-names -mrelocation-model static -mconstructor-aliases -target-cpu arm1176jzf-s -target-feature +vfp2 -target-feature +vfp2sp -target-feature -vfp3 -target-feature -vfp3d16 -target-feature -vfp3d16sp -target-feature -vfp3sp -target-feature -fp16 -target-feature -vfp4 -target-feature -vfp4d16 -target-feature -vfp4d16sp -target-feature -vfp4sp -target-feature -fp-armv8 -target-feature -fp-armv8d16 -target-feature -fp-armv8d16sp -target-feature -fp-armv8sp -target-feature -fullfp16 -target-feature +fp64 -target-feature -d32 -target-feature -neon -target-feature -sha2 -target-feature -aes -target-feature -fp16fml -target-feature +strict-align -target-abi aapcs-linux -mfloat-abi hard -fallow-half-arguments-and-returns -ffunction-sections -fdata-sections -O1 -std=c++14 -fdeprecated-macro -fno-rtti -fno-signed-char -faddrsig -fexperimental-new-pass-manager PPCISelLowering-009095.ii

1. <eof> parser at end of file
2. Code generation
3. Running pass 'Function Pass Manager' on module 'PPCISelLowering-009095.cpp'.
4. Running pass 'ARM Instruction Selection' on function '@_ZN4llvm17PPCTargetLoweringC2ERKNS_16PPCTargetMachineERKNS_12PPCSubtargetE'

This crash or assertion is fixed by the upstream commit.

MFC after: 3 days

(cherry picked from commit ada8b24d48d93f0b13209b555b64f3d355ef61d9)