[runtimes] Use llvm-libtool-darwin for runtimes build

[smeenai]

Summary

It's full featured now and we can use it for the runtimes build instead
of relying on an external libtool, which means the CMAKE_HOST_APPLE
restriction serves no purpose either now. Restrict llvm-lipo to Darwin
targets while I'm here, since it's only needed there.

[phosek]

LGTM

compiler-rt/CMakeLists.txt

if(NOT Python3_Interpreter_FOUND)
       add_executable(Python3::Interpreter IMPORTED)
       set_target_properties(Python3::Interpreter PROPERTIES
         IMPORTED_LOCATION ${Python2_EXECUTABLE})
       set(Python3_EXECUTABLE ${Python2_EXECUTABLE})
     endif()
   endif()
 
   # Ensure that fat libraries are built correctly on Darwin
-  if(CMAKE_HOST_APPLE AND APPLE)
+  if(APPLE)
     include(UseLibtool)
   endif()
 
   # Define default arguments to lit.
   set(LIT_ARGS_DEFAULT "-sv")
   if (MSVC OR XCODE)
     set(LIT_ARGS_DEFAULT "${LIT_ARGS_DEFAULT} --no-progress-bar")
   endif()

compiler-rt/lib/builtins/CMakeLists.txt

if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   include(CompilerRTUtils)
 
   load_llvm_config()
   construct_compiler_rt_default_triple()
 
   if(APPLE)
     include(CompilerRTDarwinUtils)
   endif()
-  if(CMAKE_HOST_APPLE AND APPLE)
+  if(APPLE)
     include(UseLibtool)
   endif()
   include(AddCompilerRT)
 endif()
 
 if (COMPILER_RT_STANDALONE_BUILD)
   # When compiler-rt is being built standalone, possibly as a cross-compilation
   # target, the target may or may not want position independent code. This

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

function(llvm_ExternalProject_Add name source_dir)
 
   foreach(arg ${ARG_CMAKE_ARGS})
     if(arg MATCHES "^-DCMAKE_SYSTEM_NAME=")
       string(REGEX REPLACE "^-DCMAKE_SYSTEM_NAME=(.*)$" "\\1" _cmake_system_name "${arg}")
     endif()
   endforeach()
 
   if(NOT ARG_TOOLCHAIN_TOOLS)
-    set(ARG_TOOLCHAIN_TOOLS clang lld llvm-ar llvm-lipo llvm-ranlib llvm-nm llvm-objdump)
-    if(NOT _cmake_system_name STREQUAL Darwin)
+    set(ARG_TOOLCHAIN_TOOLS clang lld llvm-ar llvm-ranlib llvm-nm llvm-objdump)
+    if(_cmake_system_name STREQUAL Darwin)
+      list(APPEND ARG_TOOLCHAIN_TOOLS llvm-libtool-darwin llvm-lipo)
+    else()
       # TODO: These tools don't fully support Mach-O format yet.
       list(APPEND ARG_TOOLCHAIN_TOOLS llvm-objcopy llvm-strip)
     endif()
   endif()
   foreach(tool ${ARG_TOOLCHAIN_TOOLS})
     if(TARGET ${tool})
       list(APPEND TOOLCHAIN_TOOLS ${tool})
 
if(lld IN_LIST TOOLCHAIN_TOOLS)
         list(APPEND compiler_args -DCMAKE_LINKER=${LLVM_RUNTIME_OUTPUT_INTDIR}/lld-link${CMAKE_EXECUTABLE_SUFFIX})
       elseif(NOT _cmake_system_name STREQUAL Darwin)
         list(APPEND compiler_args -DCMAKE_LINKER=${LLVM_RUNTIME_OUTPUT_INTDIR}/ld.lld${CMAKE_EXECUTABLE_SUFFIX})
       endif()
     endif()
     if(llvm-ar IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_AR=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-ar${CMAKE_EXECUTABLE_SUFFIX})
     endif()
+    if(llvm-libtool-darwin IN_LIST TOOLCHAIN_TOOLS)
+      list(APPEND compiler_args -DCMAKE_LIBTOOL=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-libtool-darwin${CMAKE_EXECUTABLE_SUFFIX})
+    endif()
     if(llvm-lipo IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_LIPO=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-lipo${CMAKE_EXECUTABLE_SUFFIX})
     endif()
     if(llvm-ranlib IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_RANLIB=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-ranlib${CMAKE_EXECUTABLE_SUFFIX})
     endif()
     if(llvm-nm IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_NM=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-nm${CMAKE_EXECUTABLE_SUFFIX})