[clang] [llvm] Enable ClangIR Build By Default (PR #221291)

[Douglas Yung via cfe-commits]

dyung wrote:

I bisected a failure on our Windows VS2019 build bot back to this change. Here is the failure:

https://lab.llvm.org/buildbot/#/builders/46/builds/43134
```
[3973/6860] Building CXX object projects\cross-project-tests\CMakeFiles\check-gdb-mlir-support.dir\debuginfo-tests\llvm-prettyprinters\gdb\mlir-support.cpp.obj
FAILED: projects/cross-project-tests/CMakeFiles/check-gdb-mlir-support.dir/debuginfo-tests/llvm-prettyprinters/gdb/mlir-support.cpp.obj 
C:\bin\ccache.exe C:\PROGRA~2\MICROS~1\2019\BUILDT~1\VC\Tools\MSVC\1429~1.301\bin\HostX64\x64\cl.exe  /nologo /TP -DLLVM_BUILD_STATIC -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_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IZ:\b\llvm-clang-x86_64-sie-win\build\projects\cross-project-tests -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\cross-project-tests -IZ:\b\llvm-clang-x86_64-sie-win\build\include -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\include -IZ:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\..\mlir\include -IZ:\b\llvm-clang-x86_64-sie-win\build\tools\mlir\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4146 -wd4244 -wd4267 -wd4456 -wd4457 -wd4458 -wd4459 -wd4624 -wd4100 -wd4127 -wd4505 -wd4702 -wd4245 -wd4310 -wd4701 -wd4703 -wd4389 -wd4805 -wd4577 -wd4319 -wd4324 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2  -std:c++17 -MD -UNDEBUG /EHs-c- /GR- /showIncludes /Foprojects\cross-project-tests\CMakeFiles\check-gdb-mlir-support.dir\debuginfo-tests\llvm-prettyprinters\gdb\mlir-support.cpp.obj /Fdprojects\cross-project-tests\CMakeFiles\check-gdb-mlir-support.dir\ /FS -c Z:\b\llvm-clang-x86_64-sie-win\llvm-project\cross-project-tests\debuginfo-tests\llvm-prettyprinters\gdb\mlir-support.cpp
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\..\mlir\include\mlir/IR/Location.h(200): error C2440: 'reinterpret_cast': cannot convert from 'T' to 'uintptr_t'
        with
        [
            T=uintptr_t
        ]
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\llvm\..\mlir\include\mlir/IR/Location.h(200): note: Conversion is a valid standard conversion, which can be performed implicitly or by use of static_cast, C-style cast or function-style cast
Z:\b\llvm-clang-x86_64-sie-win\llvm-project\cross-project-tests\debuginfo-tests\llvm-prettyprinters\gdb\mlir-support.cpp(29): note: see reference to function template instantiation 'mlir::OpaqueLoc mlir::OpaqueLoc::get<uintptr_t>(T,mlir::MLIRContext *)' being compiled
        with
        [
            T=uintptr_t
        ]
```
Can you take a look?

https://github.com/llvm/llvm-project/pull/221291