[llvm] [CodeGen] Use SmallVector for MBB preds/succs (PR #101948)

[Nikita Popov via llvm-commits]

nikic wrote:

```FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MIRSampleProfile.cpp.obj
sccache C:\BuildTools\VC\Tools\MSVC\14.29.30133\bin\Hostx64\x64\cl.exe  /nologo /TP -DBUILD_EXAMPLES -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 -Ilib\CodeGen -IC:\ws\src\llvm\lib\CodeGen -Iinclude -IC:\ws\src\llvm\include /DWIN32 /D_WINDOWS   /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 -w14062 -we4238 /Gw /O2 /Ob2  -MD  /EHs-c- /GR- -UNDEBUG -std:c++17 /showIncludes /Folib\CodeGen\CMakeFiles\LLVMCodeGen.dir\MIRSampleProfile.cpp.obj /Fdlib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LLVMCodeGen.pdb /FS -c C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(136): error C2440: 'return': cannot convert from 'llvm::iterator_range<llvm::MachineBasicBlock::pred_iterator>' to 'llvm::iterator_range<std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>>>'
        with
        [
            _Ty=llvm::MachineBasicBlock *
        ]
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(136): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(139): error C2440: 'return': cannot convert from 'llvm::iterator_range<llvm::MachineBasicBlock::pred_iterator>' to 'llvm::iterator_range<std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>>>'
        with
        [
            _Ty=llvm::MachineBasicBlock *
        ]
C:\ws\src\llvm\lib\CodeGen\MIRSampleProfile.cpp(139): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
```

https://github.com/llvm/llvm-project/pull/101948