[mlir] Fix cross compiling MLIR

Setting MLIR_TABLEGEN_EXE would prevent building the native tool which is used in cross-compiling

Differential Revision: https://reviews.llvm.org/D75299

Author: isuruf

mlir/CMakeLists.txt

@@ -1,7 +1,6 @@
 # MLIR project.
 set(MLIR_MAIN_SRC_DIR ${CMAKE_CURRENT_SOURCE_DIR}/include ) # --src-root
 set(MLIR_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include ) # --includedir
-set(MLIR_TABLEGEN_EXE mlir-tblgen)
 
 set(MLIR_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(MLIR_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
@@ -32,6 +31,11 @@ set(MLIR_VULKAN_RUNNER_ENABLED 0 CACHE BOOL "Enable building the mlir Vulkan run
 include_directories( "include")
 include_directories( ${MLIR_INCLUDE_DIR})
 
+# Adding tools/mlir-tblgen here as calling add_tablegen sets some variables like
+# MLIR_TABLEGEN_EXE in PARENT_SCOPE which gets lost if that folder is included
+# from another directory like tools
+add_subdirectory(tools/mlir-tblgen)
+
 add_subdirectory(include/mlir)
 add_subdirectory(lib)
 add_subdirectory(unittests)

mlir/tools/CMakeLists.txt

@@ -1,7 +1,6 @@
 add_subdirectory(mlir-cuda-runner)
 add_subdirectory(mlir-cpu-runner)
 add_subdirectory(mlir-opt)
-add_subdirectory(mlir-tblgen)
 add_subdirectory(mlir-translate)
 add_subdirectory(mlir-vulkan-runner)
 add_subdirectory(mlir-shlib)