These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

as a target-agnostic implementation to replace target-specific
XXXMCExpr::create.

Reduce direct uses of SparcMCExpr, facilitating transition to
MCSpecifierExpr in the future.

Follow the X86, Mips, and RISCV renaming.

> "Relocation modifier" suggests adjustments happen during the linker's relocation step rather than the assembler's expression evaluation.
> "Relocation specifier" is clear, aligns with Arm and IBM AIX's documentation, and fits the assembler's role seamlessly.

In addition, rename *MCExpr::getKind, which confusingly shadows the base class getKind.

Replace with forward declaration and move dependency down to source files that actually need it.

Both TargetLowering.h and TargetMachine.h are 2 of the most expensive headers (top 10) in the ClangBuildAnalyzer report when building llc.

-fuse-init-array is now the CC1 default but TargetLoweringObjectFileELF::UseInitArray still defaults to false.
The following two unknown OS target triples continue using .ctors/.dtors because InitializeELF is not called.

clang -target i386 -c a.c
clang -target x86_64 -c a.c

This cleanup fixes this as a bonus.

X86SpeculativeLoadHardeningPass::tracePredStateThroughCall can call
MCContext::createTempSymbol before TargetLoweringObjectFileELF::Initialize().
We need to call TargetLoweringObjectFileELF::Initialize() ealier.

test/CodeGen/X86/speculative-load-hardening-indirect.ll

Differential Revision: https://reviews.llvm.org/D71360

as it's causing msan failures.

This reverts commit 7899fe9da8d8df6f19ddcbbb877ea124d711c54b.

UseInitArray is now the CC1 default but TargetLoweringObjectFileELF::UseInitArray still defaults to false.
The following two unknown OS target triples continue using .ctors/.dtors because InitializeELF is not called.

clang -target i386 -c a.c
clang -target x86_64 -c a.c

This cleanup fixes this as a bonus.

Differential Revision: https://reviews.llvm.org/D71360