This patch extracts the `msg` value of the `failwithmessage` error and
uses it as the stop reason if the MSVC Runtime fails while debugging.
# Before
```
lldb.exe C:\Users\charleszablit\Developer\testing\uninit.exe -b -o 'r'
(lldb) target create "C:\\Users\\charleszablit\\Developer\\testing\\uninit.exe"
Current executable set to 'C:\Users\charleszablit\Developer\testing\uninit.exe' (x86_64).
(lldb) r
Process 9400 launched: 'C:\Users\charleszablit\Developer\testing\uninit.exe' (x86_64)
Process 9400 stopped
* thread #1, stop reason = Exception 0x80000003 encountered at address 0x7ff96516c96a
frame #0: 0x00007ff77efe20ba uninit.exe`failwithmessage(retaddr=0x00007ff77efe150f, crttype=1, errnum=3, msg="The variable 'x' is being used without being initialized.") at error.cpp:210
```
# After
```
lldb.exe C:\Users\charleszablit\Developer\testing\uninit.exe -b -o 'r'
(lldb) target create "C:\\Users\\charleszablit\\Developer\\testing\\uninit.exe"
Current executable set to 'C:\Users\charleszablit\Developer\testing\uninit.exe' (x86_64).
(lldb) r
Process 9400 launched: 'C:\Users\charleszablit\Developer\testing\uninit.exe' (x86_64)
Process 9400 stopped
* thread #1, stop reason = Run-time check failure: The variable 'x' is being used without being initialized.
frame #0: 0x00007ff77efe20ba uninit.exe`failwithmessage(retaddr=0x00007ff77efe150f, crttype=1, errnum=3, msg="The variable 'x' is being used without being initialized.") at error.cpp:210
```
fix https://github.com/llvm/llvm-project/issues/184990.
rdar://172103284
