[llvm] [llvm-lto2] Added llvm-lto2 -unified-lto descriptions (revised) (PR #155462)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Digging through the windows-bot failure,
```
2025-09-04T03:13:36.8396084Z # | C:\_work\llvm-project\llvm-project\llvm\test\LTO\Resolution\X86\unified-lto-check.ll:49:16: error: INVALIDMODE: expected string not found in input
2025-09-04T03:13:36.8397077Z # | ; INVALIDMODE: llvm-lto2: for the --unified-lto option: Cannot find option named
2025-09-04T03:13:36.8397650Z # |                ^
2025-09-04T03:13:36.8397937Z # | <stdin>:1:1: note: scanning from here
2025-09-04T03:13:36.8398465Z # | llvm-lto2.exe: for the --unified-lto option: Cannot find option named 'foo'!
2025-09-04T03:13:36.8398954Z # | ^
2025-09-04T03:13:36.8399175Z # | 
2025-09-04T03:13:36.8399428Z # | Input file: <stdin>
2025-09-04T03:13:36.8400020Z # | Check file: C:\_work\llvm-project\llvm-project\llvm\test\LTO\Resolution\X86\unified-lto-check.ll
2025-09-04T03:13:36.8400637Z # | 
2025-09-04T03:13:36.8400924Z # | -dump-input=help explains the following input dump.
2025-09-04T03:13:36.8401318Z # | 
2025-09-04T03:13:36.8401508Z # | Input was:
2025-09-04T03:13:36.8401728Z # | <<<<<<
2025-09-04T03:13:36.8402111Z # |           1: llvm-lto2.exe: for the --unified-lto option: Cannot find option named 'foo'! 
2025-09-04T03:13:36.8402728Z # | check:49     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
2025-09-04T03:13:36.8403171Z # | >>>>>>
2025-09-04T03:13:36.8403382Z # `-----------------------------
```
That's a Windows issue where llvm-lto2 has ".exe" on the end if on Windows, and doesn't on Linux. I suppose that's solveable through using an optional regex for ".exe", or just not checking for the binary name and only the error message.

https://github.com/llvm/llvm-project/pull/155462