This patch adds support for the next-generation arch15
CPU architecture to the SystemZ backend.

This includes:
- Basic support for the new processor and its features.
- Detection of arch15 as host processor.
- Assembler/disassembler support for new instructions.
- Exploitation of new instructions for code generation.
- New vector (signed|unsigned|bool) __int128 data types.
- New LLVM intrinsics for certain new instructions.
- Support for low-level builtins mapped to new LLVM intrinsics.
- New high-level intrinsics in vecintrin.h.
- Indicate support by defining  __VEC__ == 10305.

Note: No currently available Z system supports the arch15
architecture.  Once new systems become available, the
official system name will be added as supported -march name.

Autogenerate the clang/test/CodeGen/SystemZ/zvector{,2}.c
test cases to make it easier to update them in the future.

This patch is to isolate the lax vector conversions warning only for PPC,
the reason is that SystemZ wants different logic in terms of
vector bool compatibility.

Reviewed By: lei

Differential Revision: https://reviews.llvm.org/D145506

This patch is to fix some missing lax-vector-conversion warnings including
cases that involve vector bool and vector pixel, also to fix the vector
compatibility check for the warnings.

Differential Revision: https://reviews.llvm.org/D143210

Instcombine prefers this canonical form (see getPreferredVectorIndex),
as does IRBuilder when passing the index as an integer so we may as
well use the prefered form from creation.

NOTE: All test changes are mechanical with nothing else expected
beyond a change of index type from i32 to i64.

Differential Revision: https://reviews.llvm.org/D140983

Updated the RUN line in several test cases to use the new PM syntax
  opt -passes=<pipeline>
instead of the deprecated syntax
  opt -pass1 -pass2

This was not a complete cleanup in clang/test. But just a swipe using
some simple search-and-replace. Mainly for RUN lines involving
-mem2reg, -instnamer and -early-cse.

Conversion performed using the script at:
https://gist.github.com/nikic/98357b71fd67756b0f064c9517b62a34

These are only tests where no manual fixup was required.

This adds -no-opaque-pointers to clang tests whose output will
change when opaque pointers are enabled by default. This is
intended to be part of the migration approach described in
https://discourse.llvm.org/t/enabling-opaque-pointers-by-default/61322/9.

The patch has been produced by replacing %clang_cc1 with
%clang_cc1 -no-opaque-pointers for tests that fail with opaque
pointers enabled. Worth noting that this doesn't cover all tests,
there's a remaining ~40 tests not using %clang_cc1 that will need
a followup change.

Differential Revision: https://reviews.llvm.org/D123115

For a default visibility external linkage definition, dso_local is set for ELF
-fno-pic/-fpie and COFF and Mach-O. Since default clang -cc1 for ELF is similar
to -fpic ("PIC Level" is not set), this nuance causes unneeded binary format differences.

To make emitted IR similar, ELF -cc1 -fpic will default to -fno-semantic-interposition,
which sets dso_local for default visibility external linkage definitions.

To make this flip smooth and enable future (dso_local as definition default),
this patch replaces (function) `define ` with `define{{.*}} `,
(variable/constant/alias) `= ` with `={{.*}} `, or inserts appropriate `{{.*}} `.