Revert "[flang][build] Fixed paths discrovery for the out-of-tree build. (#87822)"

This reverts commit 9202984.

Author: vzakhari

flang/CMakeLists.txt

@@ -81,13 +81,12 @@ if (FLANG_STANDALONE_BUILD)
     mark_as_advanced(LLVM_ENABLE_ASSERTIONS)
   endif()
 
+  # We need a pre-built/installed version of LLVM.
+  find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_DIR}")
   # If the user specifies a relative path to LLVM_DIR, the calls to include
   # LLVM modules fail. Append the absolute path to LLVM_DIR instead.
-  get_filename_component(LLVM_DIR_ABSOLUTE ${LLVM_DIR}
-    REALPATH BASE_DIR ${CMAKE_CURRENT_BINARY_DIR})
+  get_filename_component(LLVM_DIR_ABSOLUTE ${LLVM_DIR} REALPATH)
   list(APPEND CMAKE_MODULE_PATH ${LLVM_DIR_ABSOLUTE})
-  # We need a pre-built/installed version of LLVM.
-  find_package(LLVM REQUIRED HINTS "${LLVM_DIR_ABSOLUTE}")
 
   # Users might specify a path to CLANG_DIR that's:
   #   * a full path, or
@@ -98,7 +97,7 @@ if (FLANG_STANDALONE_BUILD)
     CLANG_DIR_ABSOLUTE
     ${CLANG_DIR}
     REALPATH
-    BASE_DIR ${CMAKE_CURRENT_BINARY_DIR})
+    ${CMAKE_CURRENT_SOURCE_DIR})
   list(APPEND CMAKE_MODULE_PATH ${CLANG_DIR_ABSOLUTE})
 
   # TODO: Remove when libclangDriver is lifted out of Clang
@@ -125,14 +124,13 @@ if (FLANG_STANDALONE_BUILD)
   include(AddClang)
 
   include(TableGen)
+  find_package(MLIR REQUIRED CONFIG)
+  # Use SYSTEM for the same reasons as for LLVM includes
+  include_directories(SYSTEM ${MLIR_INCLUDE_DIRS})
   # If the user specifies a relative path to MLIR_DIR, the calls to include
   # MLIR modules fail. Append the absolute path to MLIR_DIR instead.
-  get_filename_component(MLIR_DIR_ABSOLUTE ${MLIR_DIR}
-    REALPATH BASE_DIR ${CMAKE_CURRENT_BINARY_DIR})
+  get_filename_component(MLIR_DIR_ABSOLUTE ${MLIR_DIR} REALPATH)
   list(APPEND CMAKE_MODULE_PATH ${MLIR_DIR_ABSOLUTE})
-  find_package(MLIR REQUIRED CONFIG HINTS ${MLIR_DIR_ABSOLUTE})
-  # Use SYSTEM for the same reasons as for LLVM includes
-  include_directories(SYSTEM ${MLIR_INCLUDE_DIRS})
   include(AddMLIR)
   find_program(MLIR_TABLEGEN_EXE "mlir-tblgen" ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)