[llvm] [LivePhysRegs] Make use of `MBB.liveouts()` (semi-NFC) (PR #154728)

[Dmitry Vasilyev via llvm-commits]

slydiman wrote:

> Possible fix in: #155084

Still failed.

LivePhysRegs.cpp(369): error C2440: '<function-style-cast>': cannot convert from 'llvm::Register' to 'llvm::MCRegister'

```
19.622 [3970/130/2834]Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LivePhysRegs.cpp.obj
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/LivePhysRegs.cpp.obj 
ccache C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DGTEST_HAS_RTTI=0 -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_GLIBCXX_ASSERTIONS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\buildbot\as-builder-10\lldb-x86-64\build\lib\CodeGen -IC:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\lib\CodeGen -IC:\buildbot\as-builder-10\lldb-x86-64\build\include -IC:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\include -D__OPTIMIZE__ /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4141 -wd4146 -wd4244 -wd4267 -wd4291 -wd4351 -wd4456 -wd4457 -wd4458 -wd4459 -wd4503 -wd4624 -wd4722 -wd4100 -wd4127 -wd4512 -wd4505 -wd4610 -wd4510 -wd4702 -wd4245 -wd4706 -wd4310 -wd4701 -wd4703 -wd4389 -wd4611 -wd4805 -wd4204 -wd4577 -wd4091 -wd4592 -wd4319 -wd4709 -wd5105 -wd4324 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2  -MD  /EHs-c- /GR- -UNDEBUG -std:c++17 /showIncludes /Folib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LivePhysRegs.cpp.obj /Fdlib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LLVMCodeGen.pdb /FS -c C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\lib\CodeGen\LivePhysRegs.cpp
C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\lib\CodeGen\LivePhysRegs.cpp(369): error C2440: '<function-style-cast>': cannot convert from 'llvm::Register' to 'llvm::MCRegister'
C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\lib\CodeGen\LivePhysRegs.cpp(369): note: 'llvm::MCRegister::MCRegister': ambiguous call to overloaded function
C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\include\llvm/MC/MCRegister.h(100): note: could be 'llvm::MCRegister::MCRegister(llvm::MCRegister &&)'
C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\include\llvm/MC/MCRegister.h(100): note: or       'llvm::MCRegister::MCRegister(const llvm::MCRegister &)'
C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\include\llvm/MC/MCRegister.h(38): note: or       'llvm::MCRegister::MCRegister(unsigned int)'
C:\buildbot\as-builder-10\lldb-x86-64\llvm-project\llvm\lib\CodeGen\LivePhysRegs.cpp(369): note: while trying to match the argument list '(llvm::Register)'
```

https://github.com/llvm/llvm-project/pull/154728