Set the underlying type of enum BoundsSafetyNewChecks to unsigned.

llvm::has_single_bit and llvm::countr_zero both require that the
argument type is unsigned but the default underlying type for enums
is int, which causes build errors with MSVC.

This fixes the windows build with MSVC.

```
FAILED: tools/clang/lib/Driver/CMakeFiles/obj.clangDriver.dir/BoundsSafetyArgs.cpp.obj
C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DCLANG_BUILD_STATIC -DEXPERIMENTAL_KEY_INSTRUCTIONS -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_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 -D__SHORT_FILE__=\"BoundsSafetyArgs.cpp\" -IC:\Users\hiroshi\cas\llvm-project\build\tools\clang\lib\Driver -IC:\Users\hiroshi\cas\llvm-project\clang\lib\Driver -IC:\Users\hiroshi\cas\llvm-project\clang\include -IC:\Users\hiroshi\cas\llvm-project\build\tools\clang\include -IC:\Users\hiroshi\cas\llvm-project\build\include -IC:\Users\hiroshi\cas\llvm-project\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 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2 /DNDEBUG -std:c++17 -MD  /EHs-c- /GR- /showIncludes /Fotools\clang\lib\Driver\CMakeFiles\obj.clangDriver.dir\BoundsSafetyArgs.cpp.obj /Fdtools\clang\lib\Driver\CMakeFiles\obj.clangDriver.dir\ /FS -c C:\Users\hiroshi\cas\llvm-project\clang\lib\Driver\BoundsSafetyArgs.cpp
C:\Users\hiroshi\cas\llvm-project\clang\lib\Driver\BoundsSafetyArgs.cpp(196): error C2672: 'llvm::has_single_bit': no matching overloaded function found
C:\Users\hiroshi\cas\llvm-project\llvm\include\llvm/ADT/bit.h(147): note: could be 'bool llvm::has_single_bit(T) noexcept'
C:\Users\hiroshi\cas\llvm-project\clang\lib\Driver\BoundsSafetyArgs.cpp(196): note: 'bool llvm::has_single_bit(T) noexcept': could not deduce template argument for '<unnamed-symbol>'
C:\Users\hiroshi\cas\llvm-project\llvm\include\llvm/ADT/bit.h(146): note: 'std::enable_if_t<false,void>' : Failed to specialize alias template
```
```
FAILED: tools/clang/lib/Driver/CMakeFiles/obj.clangDriver.dir/BoundsSafetyArgs.cpp.obj
C:\PROGRA~1\MICROS~1\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DCLANG_BUILD_STATIC -DEXPERIMENTAL_KEY_INSTRUCTIONS -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_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 -D__SHORT_FILE__=\"BoundsSafetyArgs.cpp\" -IC:\Users\hiroshi\cas\llvm-project\build\tools\clang\lib\Driver -IC:\Users\hiroshi\cas\llvm-project\clang\lib\Driver -IC:\Users\hiroshi\cas\llvm-project\clang\include -IC:\Users\hiroshi\cas\llvm-project\build\tools\clang\include -IC:\Users\hiroshi\cas\llvm-project\build\include -IC:\Users\hiroshi\cas\llvm-project\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 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2 /DNDEBUG -std:c++17 -MD  /EHs-c- /GR- /showIncludes /Fotools\clang\lib\Driver\CMakeFiles\obj.clangDriver.dir\BoundsSafetyArgs.cpp.obj /Fdtools\clang\lib\Driver\CMakeFiles\obj.clangDriver.dir\ /FS -c C:\Users\hiroshi\cas\llvm-project\clang\lib\Driver\BoundsSafetyArgs.cpp
C:\Users\hiroshi\cas\llvm-project\llvm\include\llvm/ADT/bit.h(158): error C2338: static_assert failed: 'Only unsigned integral types are allowed.'
C:\Users\hiroshi\cas\llvm-project\llvm\include\llvm/ADT/bit.h(158): note: the template instantiation context (the oldest one first) is
```

Author: hjyamauchi

clang/include/clang/Basic/LangOptions.h

@@ -458,7 +458,7 @@ class LangOptionsBase {
   };
 
   /* TODO(BoundsSafety) Deprecate the flag  */
-  enum BoundsSafetyNewChecks {
+  enum BoundsSafetyNewChecks : unsigned {
     BS_CHK_None = 0,
 
     BS_CHK_AccessSize = 1 << 0,          // rdar://72252593