This adds code that was previously missing from emitAutoVarAlloca to
identify when an aggregate auto var is being emitted with a constant
initializer, and the associated code that is called from emitAutoVarInit
to store the constant. This allows significantly more efficient
initialization.

This was previously committed in
https://github.com/llvm/llvm-project/pull/166850 but that change
contained an unintended modification to an unrelated test.

This reverts commit 5fc1b74af52093cd5229ba0e1c368d41735bb990.

This broke premerge (and premerge was failing on the patch itself):
1. https://lab.llvm.org/staging/#/builders/192/builds/10053
2. https://lab.llvm.org/staging/#/builders/21/builds/8268

This adds code that was previously missing from emitAutoVarAlloca to
identify when an aggregate auto var is being emitted with a constant
initializer, and the associated code that is called from emitAutoVarInit
to store the constant. This allows significantly more efficient
initialization.

Unlike the incubator, this adds the inline attribute directly to FuncOp
instead of adding the ExtraFnAttr dict.

This adds three new optional keywords to CIR: inline_always,
inline_never and inline_hint. Just like in OGCG -O0 implies inline_never
on functions withoutt the C++ `inline` keyword and no other
inlining-related attribute.

This patch also adapts all tests that use functions so they account for
LLVM attributes being attached now.

This mirrors changes from https://github.com/llvm/clangir/pull/1933

This mirrors incubator changes from https://github.com/llvm/clangir/pull/1922

This change adds support for function linkage and visibility and related
attributes. Most of the test changes are generalizations to allow
'dso_local' to be accepted where we aren't specifically testing for it.
Some tests based on CIR inputs have been updated to add 'private' to
function declarations where required by newly supported interfaces.

The dso-local.c test has been updated to add specific tests for
dso_local being set correctly, and a new test, func-linkage.cpp tests
other linkage settings.

This change sets `comdat` correctly in CIR, but it is not yet applied to
functions when lowering to LLVM IR. That will be handled in a later
change.

This adds alignment support for GlobalOp, LoadOp, and StoreOp.

Tests which failed because cir.store/cir.load now print alignment were
updated with wildcard matches, except where the alignment was relevant
to the test. Tests which check for cir.store/cir.load in cases that
don't have explicit alignment were not updated.

New tests for alignment are alignment.c, align-load.c, and
align-store.c.

This upstreams the code needed to handle CXXForRangeStmt.

We have been using the default names for global symbols to this point.
This change introduces proper name mangling for functions.

This requires introducing a CXXABI class in the CIRGenModule. Because
only target independent name mangling is handled in this patch, the
CXXABI class does not require a target-specific implementation. The
general mechanism for selecting an implementation is introduced here,
but the actual target-specific subclasses are deferred until needed.