I invoked yaml2obj with a mistyped filename and received no error
message. I nearly thought the program had succeeded, but the shell's
exit code prompt tipped me off.

Pull Request: https://github.com/llvm/llvm-project/pull/144835

#125983

To support auto-conversion on z/OS text files need to be opened as text files. These changes will fix a number of LIT failures due to text files not being converted to the internal code page.

update a number of tools so they open the text files as text files
add support in the cat.py to open a text file as a text file (Windows will continue to treat all files as binary so new lines are handled correctly)
add env var definitions to enable auto-conversion in the lit config file.

This patch replaces uses of StringRef::{starts,ends}with with
StringRef::{starts,ends}_with for consistency with
std::{string,string_view}::{starts,ends}_with in C++20.

I'm planning to deprecate and eventually remove
StringRef::{starts,ends}with.

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

If you're having trouble getting a yaml2obj macro expansion to do what
you want, it's useful to be able to print the output of the
preprocessing to see what your macros expanded to //before// going
into the YAML processing phase.

yaml2obj has its own preprocessing system which isn't the same as any
other well-known thing like cpp. So there's no way to do this macro
expansion via another tool: yaml2obj will have to do it itself.

In this commit I add an `-E` flag to yaml2obj to do that.

Differential Revision: https://reviews.llvm.org/D130981

Differential Revision: https://reviews.llvm.org/D114538

Currently we have to override all macros that are declared. But in many
cases it is convenient to use default values and to override only
a particular one or two.

This provides a way to set a default value for any macro:

```
Symbols:
  - Name: [[FOO=foo]]
```

Differential revision: https://reviews.llvm.org/D82455

Multiple times we faced an issue of huge outputs due to unexpected behavior
or incorrect test cases. The last one was https://reviews.llvm.org/D80629#2073066.

This patch limits the output to 10 Mb for ELF and introduces the --max-size to change this
limit.

I've tried to keep the implementation non-intrusive.

The current logic we have is that we prepare section content in a buffer first and write
it to the output later. This patch checks the available limit on each writing attempt to this buffer
and stops writing when the limit is reached and raises the internal error flag.
Later, this flag is is checked before the actual writing to a file happens and
an error is reported.

Differential revision: https://reviews.llvm.org/D81258