When running a process that would exit before LLDB could stop the
target, it would try to interpret (and subsequently format) the exit
code as a Win32 error. However, processes on Windows won't return Win32
errors in that case. They will often return an
[NTSTATUS](https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-erref/596a1078-e883-4972-9bbc-49e60bebca55).
One common case for this to occur is when a DLL is missing. In that
case, the process will start successfully, but it will exit with
`STATUS_DLL_NOT_FOUND`.
LLDB would previously return "unknown error", because it tried to
[`FormatMessage`](https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-formatmessage)
`0xC0000135` which doesn't work, so it fell back to "unknown error".

This PR changes the error to be the string "Process prematurely exited
with {0:x}" and doesn't try to format the exit code. One could
`FormatMessage` an `NTSTATUS` by passing `FORMAT_MESSAGE_FROM_HMODULE`
and a handle to `ntdll.dll`, however, I don't think we can get the
required format arguments (e.g. the missing DLL name - `%hs`).

ReadProcessMemory will not perform the read if part of the memory is
unreadable (and even though the API has a `number_of_bytes_read`
argument). To make this work, I explicitly inspect the memory region
being read and only read the accessible part.

This patch removes all of the Set.* methods from Status.

This cleanup is part of a series of patches that make it harder use the
anti-pattern of keeping a long-lives Status object around and updating
it while dropping any errors it contains on the floor.

This patch is largely NFC, the more interesting next steps this enables
is to:
1. remove Status.Clear()
2. assert that Status::operator=() never overwrites an error
3. remove Status::operator=()

Note that step (2) will bring 90% of the benefits for users, and step
(3) will dramatically clean up the error handling code in various
places. In the end my goal is to convert all APIs that are of the form

`    ResultTy DoFoo(Status& error)
`
to

`    llvm::Expected<ResultTy> DoFoo()
`
How to read this patch?

The interesting changes are in Status.h and Status.cpp, all other
changes are mostly

` perl -pi -e 's/\.SetErrorString/ = Status::FromErrorString/g' $(git
grep -l SetErrorString lldb/source)
`
plus the occasional manual cleanup.

Resubmission of https://reviews.llvm.org/D130309 with the 2 patches that fixed the linux buildbot, and new windows fixes.

The FileSpec APIs allow users to modify instance variables directly by getting a non const reference to the directory and filename instance variables. This makes it impossible to control all of the times the FileSpec object is modified so we can clear cached member variables like m_resolved and with an upcoming patch caching if the file is relative or absolute. This patch modifies the APIs of FileSpec so no one can modify the directory or filename instance variables directly by adding set accessors and by removing the get accessors that are non const.

Many clients were using FileSpec::GetCString(...) which returned a unique C string from a ConstString'ified version of the result of GetPath() which returned a std::string. This caused many locations to use this convenient function incorrectly and could cause many strings to be added to the constant string pool that didn't need to. Most clients were converted to using FileSpec::GetPath().c_str() when possible. Other clients were modified to use the newly renamed version of this function which returns an actualy ConstString:

ConstString FileSpec::GetPathAsConstString(bool denormalize = true) const;

This avoids the issue where people were getting an already uniqued "const char *" that came from a ConstString only to put the "const char *" back into a "ConstString" object. By returning the ConstString instead of a "const char *" clients can be more efficient with the result.

The patch:
- Removes the non const GetDirectory() and GetFilename() get accessors
- Adds set accessors to replace the above functions: SetDirectory() and SetFilename().
- Adds ClearDirectory() and ClearFilename() to replace usage of the FileSpec::GetDirectory().Clear()/FileSpec::GetFilename().Clear() call sites
- Fixed all incorrect usage of FileSpec::GetCString() to use FileSpec::GetPath().c_str() where appropriate, and updated other call sites that wanted a ConstString to use the newly returned ConstString appropriately and efficiently.

Differential Revision: https://reviews.llvm.org/D130549

Previously we recorded AllocationBase as the base address of the region
we get from VirtualQueryEx. However, this is the base of the allocation,
which can later be split into more regions.

So you got stuff like:
[0x00007fff377c0000-0x00007fff377c1000) r-- PECOFF header
[0x00007fff377c0000-0x00007fff37840000) r-x .text
[0x00007fff377c0000-0x00007fff37870000) r-- .rdata

Where all the base addresses were the same.

Instead, use BaseAddress as the base of the region. So we get:
[0x00007fff377c0000-0x00007fff377c1000) r-- PECOFF header
[0x00007fff377c1000-0x00007fff37840000) r-x .text
[0x00007fff37840000-0x00007fff37870000) r-- .rdata

https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-memory_basic_information

The added test checks for any overlapping regions which means
if we get the base or size wrong it'll fail. This logic
applies to any OS so the test isn't restricted to Windows.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D129272

This comment became outdated in 053eb35651906e693906fad6c695fce11415ade7
(but was moved along); that commit moved the code and the comment
to a separate function, with a separate local variable
`num_of_bytes_read`. On error, the possibly garbage value is never
copied back to the caller's reference, thus the comment is no longer
relevant (and slightly confusing as is).

Differential Revision: https://reviews.llvm.org/D128226

This reverts commit 6f5ce43b433706c3ae5c37022d6c0964b6bfadf8 due to
build failure on Windows.