[llvm] [BOLT] Enable standalone build (PR #97130)

[Konrad Kleine via llvm-commits]

================
@@ -9,6 +20,42 @@ set(CMAKE_CXX_STANDARD 17)
 # Add path for custom modules.
 list(INSERT CMAKE_MODULE_PATH 0 "${BOLT_SOURCE_DIR}/cmake/modules")
 
+include(GNUInstallDirs)
+
+# 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 "${LLVM_DIR}")
+
+  set(LLVM_MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm" CACHE PATH "Path to LLVM source tree")
+  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${LLVM_LIBDIR_SUFFIX})
+
+  include(AddLLVM)
+  include(TableGen)
+  include_directories(${LLVM_INCLUDE_DIRS})
+  link_directories("${LLVM_LIBRARY_DIR}")
+
+  set( CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_INSTALL_BINDIR}" )
+  set( CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_INSTALL_LIBDIR}/${LLVM_LIBDIR_SUFFIX}" )
+  set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_INSTALL_LIBDIR}/${LLVM_LIBDIR_SUFFIX}")
----------------
kwk wrote:

In [clang](https://github.com/llvm/llvm-project/blob/53c7fe50d869386459226aeac5ec72ee918737c9/clang/CMakeLists.txt#L91-L92), this part looks like this:

```
  set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
  set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
```

Notice the missing `lib` in your code.

https://github.com/llvm/llvm-project/pull/97130