[llvm] [BOLT] Enable standalone build (PR #87196)

[Amir Ayupov via llvm-commits]

================
@@ -7,6 +18,122 @@ set(CMAKE_CXX_STANDARD 17)
 # Add path for custom modules.
 list(INSERT CMAKE_MODULE_PATH 0 "${BOLT_SOURCE_DIR}/cmake/modules")
 
+# standalone build, copied from clang
+if(BOLT_BUILT_STANDALONE)
+  set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard to conform to")
+  set(CMAKE_CXX_STANDARD_REQUIRED YES)
+  set(CMAKE_CXX_EXTENSIONS NO)
+
+  if(NOT MSVC_IDE)
+    set(LLVM_ENABLE_ASSERTIONS ${ENABLE_ASSERTIONS}
+      CACHE BOOL "Enable assertions")
+    # Assertions should follow llvm-config's.
+    mark_as_advanced(LLVM_ENABLE_ASSERTIONS)
+  endif()
+
+  find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_DIR}")
+  list(APPEND CMAKE_MODULE_PATH "${LLVM_DIR}")
+
+  # Turn into CACHE PATHs for overwritting
+  set(LLVM_INCLUDE_DIRS ${LLVM_INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
+  set(LLVM_BINARY_DIR "${LLVM_BINARY_DIR}" CACHE PATH "Path to LLVM build tree")
+  set(LLVM_MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm" CACHE PATH "Path to LLVM source tree")
+  set(LLVM_TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}" CACHE PATH "Path to llvm/bin")
+  set(LLVM_LIBRARY_DIR "${LLVM_LIBRARY_DIR}" CACHE PATH "Path to llvm/lib")
+
+  find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}
+    NO_DEFAULT_PATH)
+
+  # They are used as destination of target generators.
+  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()
+
+  option(LLVM_INSTALL_TOOLCHAIN_ONLY
+    "Only include toolchain files in the 'install' target." OFF)
+
+  option(LLVM_FORCE_USE_OLD_TOOLCHAIN
+    "Set to ON to force using an old, unsupported host toolchain." OFF)
+  option(CLANG_ENABLE_BOOTSTRAP "Generate the clang bootstrap target" OFF)
+  option(LLVM_ENABLE_LIBXML2 "Use libxml2 if available." ON)
----------------
aaupov wrote:

Does BOLT really need these options? Can you please check if they are used in our build?

https://github.com/llvm/llvm-project/pull/87196