The current error message doesn't give sufficient details to help with
debugging. This patch will log the operand values that are conflicting.
After this patch the output is of the form:
```
'Large Data Threshold': IDs have conflicting values: 'i32 101' from /usr/local/home/llvm-project/build/test/LTO/X86/Output/largedatathreshold-3.ll.tmp1.o, and 'i32 100' from ld-temp.o
```
Conflicting module flags leads to a proper error for regular LTO but a crash
(report_fatal_error) for ThinLTO. Switch to createStringError to fix the crash
and match regular LTO.