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.

Add RISC-V support for XRay. The RV64 implementation has been tested in
both QEMU and in our hardware environment.

Currently this requires D and C extensions, but since both RV64GC and
RVA22/RVA23 are becoming mainstream, I don't think this requirement will
be a big problem.

Based on the previous work by @a-poduval :
https://reviews.llvm.org/D117929

---------

Co-authored-by: Ashwin Poduval <ashwin.poduval@gmail.com>

Only support patching FunctionEntry/FunctionExit/FunctionTailExit for now.

Reviewed By: MaskRay, xen0n
Co-Authored-By: zhanglimin <zhanglimin@loongson.cn>

Differential Revision: https://reviews.llvm.org/D140727

I also ran `git clang-format` to get the headers in the right order for
the new location, which has changed the order of other headers in two
files.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

These source files no longer use None, so they do not need to include
None.h.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated.  The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

std::size, introduced in C++17, allows us to directly obtain the
number of elements of an array.

These are some usage examples for `Expected<T>::moveInto()`.

Differential Revision: https://reviews.llvm.org/D112280