[Unity] Fix the ambiguity issue in vDevice constructor on Mac with Apple clang version 14.0.3

[sunggg]

PR #15447 introduces vDevice and currently, it causes compilation failure on my Mac with the following error:

sung@spark-mbp build % gcc --version                                          
Apple clang version 14.0.3 (clang-1403.0.22.14.1)
Target: x86_64-apple-darwin22.3.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

/Users/sung/tvm/src/ir/global_info.cc:33:25: error: addition of default argument on redeclaration makes this constructor a default constructor
VDevice::VDevice(Target tgt = {}, int dev_id = -1, MemoryScope mem_scope = {}) {
                        ^   ~~~~
/Users/sung/tvm/include/tvm/ir/global_info.h:97:20: note: previous declaration is here
  TVM_DLL explicit VDevice(Target tgt, int dev_id, MemoryScope mem_scope);
                   ^
1 error generated.
make[2]: *** [CMakeFiles/tvm_objs.dir/src/ir/global_info.cc.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/tvm_objs.dir/all] Error 2

This occurs due to the ambiguity with the default constructor defined within TVM_DEFINE_OBJECT_REF_METHODS.
Therefore, this PR eliminates such ambiguity by explicitly calling the constructor.
Since it requires explicit passing of the default arguments, I'd like to find a way to support previous usage (e.g., VDevice()) without the ambiguity. But I don't have good idea at the moment unfortunately.
cc. @yongwww

[tvm-bot]

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• cc @quic-sanirudh _{See #10317 for details}

_{Generated by tvm-bot}

[yongwww]

Thanks @sunggg for the hot fix! To pass the CI tests, please change this line to if (n->vdevice.defined() && n->vdevice.value()->target.defined()) {. I can submit fix to your branch for this hotfix if some other tests fail