Allow for using LLVM from Homebrew and include its libc++

CMakeLists.txt

@@ -123,9 +123,11 @@ if (ENABLE_LTO)
 		if (NOT LLD STREQUAL "LLD-NOTFOUND")
 			add_link_options(-fuse-ld=lld)
 		endif()
+		if (NOT APPLE)
 			set(CMAKE_AR "llvm-ar")
 			set(CMAKE_RANLIB "llvm-ranlib")
 		endif()
+	endif()
 endif()
 
 find_program(CCACHE "ccache")

cmake/Toolchain-Homebrew-LLVM.cmake

@@ -0,0 +1,12 @@
+# Toolchain file for building with Homebrew's LLVM on macOS
+# This is useful on 10.14 where std::filesystem is not supported.
+
+set(CMAKE_C_COMPILER /usr/local/opt/llvm/bin/clang)
+set(CMAKE_CXX_COMPILER /usr/local/opt/llvm/bin/clang++)
+
+add_link_options(-L/usr/local/opt/llvm/lib)
+
+# LLVM in Homebrew is built with latest Xcode which has a newer linker than
+# what is bundled in the default install of Xcode Command Line Tools, so we
+# override it to prevent it passing flags not supported by the system's ld.
+add_link_options(-mlinker-version=450)

tools/mac-libs.rb

@@ -56,6 +56,10 @@ def expand_load_path(lib, path)
         file = $fallback_rpaths
           .map { |it| File.join(it, file_name) }
           .find { |it| File.exist? it }
+	if file == nil
+          path = File.join(File.dirname(lib), file_name)
+          file = path if File.exist? path
+        end
         return file, :rpath if file
       when "executable_path"
         file = File.join(File.dirname(executable), file_name)
@@ -85,7 +89,6 @@ def install_name_tool(exec, action, path1, path2 = nil)
   args = ["-#{action.to_s}", path1]
   args << path2 if path2 != nil
 
-  FileUtils.chmod("u+w", exec)
   out, status = Open3.capture2e("install_name_tool", *args, exec)
   if status != 0
     puts out
@@ -129,6 +132,7 @@ def fixup_libs(prog, orig_path)
       next if File.exist? File.join(frameworks_dir, fwname)
       expath, _ = expand_load_path(orig_path, framework)
       FileUtils.cp_r(expath, frameworks_dir, preserve: true)
+      FileUtils.chmod_R("u+w", File.join(frameworks_dir, fwname))
       fixup_libs File.join(frameworks_dir, fwname, fwlib), libpath
     else
       libname = File.basename(libpath)
@@ -141,6 +145,7 @@ def fixup_libs(prog, orig_path)
       next if File.exist? dest
       expath, _ = expand_load_path(orig_path, libpath)
       FileUtils.copy expath, frameworks_dir
+      FileUtils.chmod("u+w", dest)
       fixup_libs dest, libpath
     end
   end