[mlir] mlir-opt: Fix linking after 7c4e8c6a .

Without this, undefined refernces to the LLVMIR translations:
```
ld: mlir-opt.cpp:(.text.startup.main+0x49): undefined reference to `mlir::registerAMXDialectTranslation(mlir::DialectRegistry&)'
ld: mlir-opt.cpp:(.text.startup.main+0x51): undefined reference to `mlir::registerArmSMEDialectTranslation(mlir::DialectRegistry&)'
ld: mlir-opt.cpp:(.text.startup.main+0x59): undefined reference to `mlir::registerArmSVEDialectTranslation(mlir::DialectRegistry&)'
ld: mlir-opt.cpp:(.text.startup.main+0x81): undefined reference to `mlir::registerOpenACCDialectTranslation(mlir::DialectRegistry&)'
ld: mlir-opt.cpp:(.text.startup.main+0x89): undefined reference to `mlir::registerOpenMPDialectTranslation(mlir::DialectRegistry&)'
ld: mlir-opt.cpp:(.text.startup.main+0x99): undefined reference to `mlir::registerX86VectorDialectTranslation(mlir::DialectRegistry&)'
```

Reviewed By: stellaraccident

Differential Revision: https://reviews.llvm.org/D158606