Removing LLVM blockers for Rust compiler

High Priority bugs in LLVM for the Rust compiler indicates that we need to ask Huawei's help to resolve these problems.

At the following thread a heated discussion has revealed 5-10 issues that need to be addressed.

List of features as candidates for Huawei's LLVM team

A lot of these have examples on godbolt. Add --emit llvm-ir to the flags to show the LLVM IR that rustc is generating.

Rust insufficiently optimizes loop { match { } } state machines

rust-lang/rust#80630

align_to prefix max length not taken into account in optimization

Unnecessary auto-vectorization ie emitted when the max length of a loop is always less than 16.

rust-lang/rust#72356

Comparison of Option<NonZeroU*> is not fully optimized

rust-lang/rust#49892

cmov conversion hurts binary search performance

rust-lang/rust#53823

https://bugs.llvm.org/show_bug.cgi?id=40027

&& operator chains (and ||, possibly) generates unoptimizable LLVM IR

rust-lang/rust#83623

https://bugs.llvm.org/show_bug.cgi?id=51211

rust can't serialize 11 fields efficiently

https://rust.godbolt.org/z/hfG734fGf

rust-lang/rust#45068

Compiler generating extra memcpy, inconsistently depending on used types

rust-lang/rust#85094

https://godbolt.org/z/d5PKx3b1d

Different (suboptimal) assembly generated for match expr vs if-else ifs

rust-lang/rust#100562

Rust 1.56.0+ no longer recognizes boundary checks as avoiding division overflow panic

rust-lang/rust#99960

https://godbolt.org/z/x95rGbW4j

Suboptimal codegen for snippet with Armv7 target

rust-lang/rust#98157

https://godbolt.org/z/ehxabaq38

Resolved issues

Inefficient compilation of ? operator

rust-lang/rust#88616

This comment shows a simple example of this issue:

rust-lang/rust#88616 (comment)

NonZero prevents values from being const-propagated properly

Specifically the example in this comment is not being optimized.

rust-lang/rust#51346 (comment)

See the godbolt examples here:

https://godbolt.org/z/fPjn9zxo6

SimplifyCFG doesn't preserve information about exhaustive switch

The example LLVM IR that fails to optimize is in this comment:

rust-lang/rust#85133 (comment)