[lldb] Unify CalculateMD5 return types (#91029)

This is a retake of https://github.com/llvm/llvm-project/pull/90921
which got reverted because I forgot to modify the CalculateMD5 unit test
I had added in https://github.com/llvm/llvm-project/pull/88812

The prior failing build is here:
https://lab.llvm.org/buildbot/#/builders/68/builds/73622
To make sure this error doesn't happen, I ran `ninja
ProcessGdbRemoteTests` and then executed the resulting test binary and
observed the `CalculateMD5` test passed.

# Overview
In my previous PR: https://github.com/llvm/llvm-project/pull/88812,
@JDevlieghere suggested to match return types of the various calculate
md5 functions.

This PR achieves that by changing the various calculate md5 functions to
return `llvm::ErrorOr<llvm::MD5::MD5Result>`.
 
The suggestion was to go for `std::optional<>` but I opted for
`llvm::ErrorOr<>` because local calculate md5 was already possibly
returning `ErrorOr`.

To make sure I didn't break the md5 calculation functionality, I ran
some tests for the gdb remote client, and things seem to work.

# Testing
1. Remote file doesn't exist

![image](https://github.com/llvm/llvm-project/assets/1326275/b26859e2-18c3-4685-be8f-c6b6a5a4bc77)

1. Remote file differs

![image](https://github.com/llvm/llvm-project/assets/1326275/cbdb3c58-555a-401b-9444-c5ff4c04c491)

1. Remote file matches

![image](https://github.com/llvm/llvm-project/assets/1326275/07561572-22d1-4e0a-988f-bc91b5c2ffce)

## Test gaps
Unfortunately, I had to modify
`lldb/source/Plugins/Platform/MacOSX/PlatformDarwinDevice.cpp` and I
can't test the changes there. Hopefully, the existing test suite / code
review from whomever is reading this will catch any issues.

1 files changed, 19 insertions, 11 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index 7498a070c..db9fb37 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -3418,8 +3418,8 @@ bool GDBRemoteCommunicationClient::GetFileExists(
   return true;
 }
 
-bool GDBRemoteCommunicationClient::CalculateMD5(
-    const lldb_private::FileSpec &file_spec, uint64_t &low, uint64_t &high) {
+llvm::ErrorOr<llvm::MD5::MD5Result> GDBRemoteCommunicationClient::CalculateMD5(
+    const lldb_private::FileSpec &file_spec) {
   std::string path(file_spec.GetPath(false));
   lldb_private::StreamString stream;
   stream.PutCString("vFile:MD5:");
@@ -3428,11 +3428,11 @@ bool GDBRemoteCommunicationClient::CalculateMD5(
   if (SendPacketAndWaitForResponse(stream.GetString(), response) ==
       PacketResult::Success) {
     if (response.GetChar() != 'F')
-      return false;
+      return std::make_error_code(std::errc::illegal_byte_sequence);
     if (response.GetChar() != ',')
-      return false;
+      return std::make_error_code(std::errc::illegal_byte_sequence);
     if (response.Peek() && *response.Peek() == 'x')
-      return false;
+      return std::make_error_code(std::errc::no_such_file_or_directory);
 
     // GDBRemoteCommunicationServerCommon::Handle_vFile_MD5 concatenates low and
     // high hex strings. We can't use response.GetHexMaxU64 because that can't
@@ -3455,25 +3455,33 @@ bool GDBRemoteCommunicationClient::CalculateMD5(
     auto part =
         response.GetStringRef().substr(response.GetFilePos(), MD5_HALF_LENGTH);
     if (part.size() != MD5_HALF_LENGTH)
-      return false;
+      return std::make_error_code(std::errc::illegal_byte_sequence);
     response.SetFilePos(response.GetFilePos() + part.size());
 
+    uint64_t low;
     if (part.getAsInteger(/*radix=*/16, low))
-      return false;
+      return std::make_error_code(std::errc::illegal_byte_sequence);
 
     // Get high part
     part =
         response.GetStringRef().substr(response.GetFilePos(), MD5_HALF_LENGTH);
     if (part.size() != MD5_HALF_LENGTH)
-      return false;
+      return std::make_error_code(std::errc::illegal_byte_sequence);
     response.SetFilePos(response.GetFilePos() + part.size());
 
+    uint64_t high;
     if (part.getAsInteger(/*radix=*/16, high))
-      return false;
+      return std::make_error_code(std::errc::illegal_byte_sequence);
 
-    return true;
+    llvm::MD5::MD5Result result;
+    llvm::support::endian::write<uint64_t, llvm::endianness::little>(
+        result.data(), low);
+    llvm::support::endian::write<uint64_t, llvm::endianness::little>(
+        result.data() + 8, high);
+
+    return result;
   }
-  return false;
+  return std::make_error_code(std::errc::operation_canceled);
 }
 
 bool GDBRemoteCommunicationClient::AvoidGPackets(ProcessGDBRemote *process) {