[CMake] Support building Fuchsia toolchain on Darwin

[phosek]

Summary

This is already supported on Linux but on Darwin it requires some extra flags.

[phosek]

cmake/caches/Fuchsia.cmake

3

This is only needed because the first stage compiler is building host builtins which on Darwin require extra architecture support. I don't know if there is a way to disable this behavior? One option I can think of would be to set LLVM_BUILTIN_TARGETS to "". Alternative would be to add a new CMake option, e.g. LLVM_INCLUDE_RUNTIMES.

[phosek]

cmake/caches/Fuchsia.cmake

3

I've implemented that option in D31060.

[phosek]

cmake/caches/Fuchsia.cmake

3

Turned out this is not going to work since the runtimes build is apparently needed by the second stage compiler.

[beanz]

cmake/caches/Fuchsia.cmake

3

You can disable the embedded builtins by turning off COMPILER_RT_ENABLE_IOS. There are corresponding WATCHOS and TVOS options that you might want to hit off as well. They default off, but defaults do change sometimes.

[phosek]

Thanks, this is exactly what I was looking for!

[beanz]

Looks great!

cmake/caches/Fuchsia-stage2.cmake

 set(CLANG_PLUGIN_SUPPORT OFF CACHE BOOL "")
 
 set(LLVM_ENABLE_LTO ON CACHE BOOL "")
 if(NOT APPLE)
   set(LLVM_ENABLE_LLD ON CACHE BOOL "")
   set(CLANG_DEFAULT_LINKER lld CACHE STRING "")
 endif()
 
+if(APPLE)
+  set(LLDB_CODESIGN_IDENTITY "" CACHE STRING "")
+endif()
+
 set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "")
 set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O2 -gline-tables-only -DNDEBUG" CACHE STRING "")
 set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O2 -gline-tables-only -DNDEBUG" CACHE STRING "")
 
 set(LLVM_BUILTIN_TARGETS "x86_64-fuchsia-none;aarch64-fuchsia-none" CACHE STRING "")
 set(BUILTINS_x86_64-fuchsia-none_CMAKE_SYSROOT ${FUCHSIA_SYSROOT} CACHE STRING "")
 set(BUILTINS_x86_64-fuchsia-none_CMAKE_SYSTEM_NAME Fuchsia CACHE STRING "")
 set(BUILTINS_aarch64-fuchsia-none_CMAKE_SYSROOT ${FUCHSIA_SYSROOT} CACHE STRING "")

cmake/caches/Fuchsia.cmake

 # This file sets up a CMakeCache for a Fuchsia toolchain build.
 
 set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
 
 set(PACKAGE_VENDOR Fuchsia CACHE STRING "")
 
 set(LLVM_INCLUDE_EXAMPLES OFF CACHE BOOL "")
 set(LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
 set(LLVM_INCLUDE_DOCS OFF CACHE BOOL "")
 set(CLANG_INCLUDE_TESTS OFF CACHE BOOL "")
 set(LLVM_ENABLE_ZLIB OFF CACHE BOOL "")
 set(LLVM_ENABLE_BACKTRACES OFF CACHE BOOL "")
 set(CLANG_PLUGIN_SUPPORT OFF CACHE BOOL "")
 
 set(CMAKE_BUILD_TYPE Release CACHE STRING "")
 
 set(BOOTSTRAP_LLVM_ENABLE_LTO ON CACHE BOOL "")
 if(NOT APPLE)
   set(BOOTSTRAP_LLVM_ENABLE_LLD ON CACHE BOOL "")
+else()
+  set(COMPILER_RT_ENABLE_IOS OFF CACHE BOOL "")
+  set(COMPILER_RT_ENABLE_TVOS OFF CACHE BOOL "")
+  set(COMPILER_RT_ENABLE_WATCHOS OFF CACHE BOOL "")
 endif()
 
 set(CLANG_BOOTSTRAP_TARGETS
   check-all
   check-llvm
   check-clang
   llvm-config
   test-suite