to align with targets that have made the transition.

* Use MCAsmInfo::printSpecifierExpr instead of MCExpr::print.
* Replace PPCMCExpr with MCSpecifierExpr.

Prepare for removing PPCMCExpr. Adopt the newer naming convention with
AMDGPU/WebAssembly/VE/M68k.

Add some intrinsics and LIT tests for PPC dmr insert/extract
instructions.

Follow the X86 and Mips 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’s usage, and fits the assembler's role seamlessly.

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

Most changes are mechanic, except:

* ELFObjectWriter::shouldRelocateWithSymbol: .TOC.@tocbase does not
  register the undefined symbol.  Move the handling into the
  Sym->isUndefined() code path.
* ELFObjectWriter::fixSymbolsInTLSFixups's VK_PPC* cases are moved to
  PPCELFObjectWriter::getRelocType. We should do similar refactoring
  for other targets and eventually remove fixSymbolsInTLSFixups.

In the future, we should classify PPCMCExpr similar to AArch64MCExpr.

Replace it with a forward declaration instead. Analysis.h is pulled in
by all passes, but not all passes need to access the module.

Under some circumstance (library loaded with the main program), TLS
initial-exec model can be applied to local-dynamic access(es). We
could use some simple heuristic to decide the update at function level:
* If there is equal or less than a number of TLS local-dynamic access(es)
in the function, use TLS initial-exec model. (the threshold which default to
1 is controlled by hidden option)

Following the aix-small-local-exec-tls target attribute, this patch adds
a target attribute for an AIX-specific option in llc that informs the
compiler that it can use a faster access sequence for the local-dynamic
TLS model (formally named aix-small-local-dynamic-tls) when TLS
variables are less than ~32KB in size.

The patch either produces an addi/la with a displacement off of module
handle (return value from .__tls_get_mod) when the address is
calculated, or it produces an addi/la followed by a load/store when the
address is calculated and used for further accesses.

---------

Co-authored-by: Amy Kwan <amy.kwan1@ibm.com>