Now when building llvm-solid with `-DMLIR_ENABLE_NVPTXCOMPILER=ON`,
there will be an absolute path (`/path/to/libnvptxcompiler_static.a`) in
MLIRNVVMTarget dependencies (in
`/build/path/install/lib/cmake/mlir/MLIRTargets.cmake`). For example,
```cmake
set_target_properties(MLIRNVVMTarget PROPERTIES
INTERFACE_LINK_LIBRARIES "MLIRIR;MLIRExecutionEngineUtils;MLIRSupport;MLIRGPUDialect;MLIRTargetLLVM;MLIRNVVMToLLVMIRTranslation;LLVMSupport;/path/to/libnvptxcompiler_static.a"
)
```
If downstream project uses pre-built llvm and depends on MLIRNVVMTarget,
it may fail to build due to the absence of the
`libnvptxcompiler_static.a` absolute path.
After this commit, there will no absolute path in
`/build/path/install/lib/cmake/mlir/MLIRTargets.cmake`
```cmake
set_target_properties(MLIRNVVMTarget PROPERTIES
INTERFACE_LINK_LIBRARIES "MLIRIR;MLIRExecutionEngineUtils;MLIRSupport;MLIRGPUDialect;MLIRTargetLLVM;MLIRNVVMToLLVMIRTranslation;LLVMSupport;\$<LINK_ONLY:MLIR_NVPTXCOMPILER_LIB>"
)
```
Then downstream project can modify `libnvptxcompiler_static.a` path and
use cmake to build. For example,
```cmake
# find_library(...)
add_library(MLIR_NVPTXCOMPILER_LIB STATIC IMPORTED GLOBAL)
set_property(TARGET MLIR_NVPTXCOMPILER_LIB PROPERTY IMPORTED_LOCATION ${...})
```
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