[mlir] [test] Fix missing SHLIB definition in standalone builds (#120907)

Define the `LLVM_SHLIB_OUTPUT_INTDIR` variable that is used by
`configure_lit_site_cfg` to fill `SHLIBDIR`. This fixes tool tests that
would otherwise be unable to find MLIR's runtime shared libraries (e.g.
`libmlir_runner_utils.so`). The logic is copied verbatim from Clang.

Author: mgorny

mlir/CMakeLists.txt

@@ -36,6 +36,15 @@ if(MLIR_STANDALONE_BUILD)
     "${CMAKE_CURRENT_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}")
   set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/bin")
 
+  # These definitions are needed to fill SHLIBDIR in tests.
+  set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
+  set(LLVM_LIBRARY_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
+  if(WIN32 OR CYGWIN)
+    # DLL platform -- put DLLs into bin.
+    set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_RUNTIME_OUTPUT_INTDIR})
+  else()
+    set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
+  endif()
   set(LLVM_LIT_ARGS "-sv" CACHE STRING "Default options for lit")
 endif()