[compiler-rt][builtins] build the macOS compiler-rt built-ins with Mac Catalyst support

[arphaman]

Summary

This patch extends compiler-rt's cmake config to build macOS builtins with both macOS and Mac Catalyst support. This is done by telling the compiler to emit macho files with two build version load commands. This is the follow-up to the clang driver support here: https://reviews.llvm.org/D118862

MachO uses two build version load commands to represent an object file / binary that is targeting both the macOS target,
and the Mac Catalyst target. At runtime, a dynamic library that supports both targets can be loaded from either a native
macOS or a Mac Catalyst app on a macOS system. We want to add support to this to upstream to LLVM to be able to build
compiler-rt for both targets, to finish the complete support for the Mac Catalyst platform, which is right now targetable
by upstream clang, but the compiler-rt bits aren't supported because of the lack of this multiple build version support.

[bc-lee]

Hi, I built and tested clang using this patch and https://reviews.llvm.org/D118862. It works great.
The current patch adds the -darwin-target-variant flag to all object files for MacOS targets in the compiler_rt's builtin library. However, users building compiler_rt may have compilers that don't support such flag, so it would be nice to have a CMake option to enable compiler flags like COMPILER_RT_ENABLE_CATALYST.

[arphaman]

In D118875#3296030, @bc-lee wrote:

Hi, I built and tested clang using this patch and https://reviews.llvm.org/D118862. It works great.
The current patch adds the -darwin-target-variant flag to all object files for MacOS targets in the compiler_rt's builtin library. However, users building compiler_rt may have compilers that don't support such flag, so it would be nice to have a CMake option to enable compiler flags like COMPILER_RT_ENABLE_CATALYST.

Good point. I will update the patch and add detection for the Mac catalyst support that detects if clang supports it with a flag .

[arphaman]

Add checking for -darwin-target-variant support

[ravikandhadai]

LGTM. Thanks Alex.

[thakis]

Is landing this blocked on anything?

[arphaman]

No, I will land it today.

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

if ("${LIB_OS}" MATCHES ".*sim$")
     # Pass an explicit -simulator environment to the -target option to ensure
     # that we don't rely on the architecture to infer whether we're building
     # for the simulator.
     string(REGEX REPLACE "sim" "" base_os "${LIB_OS}")
     list(APPEND builtin_cflags
          -target "${LIB_ARCH}-apple-${base_os}${DARWIN_${LIBOS}_BUILTIN_MIN_VER}-simulator")
   endif()
 
+  if ("${COMPILER_RT_ENABLE_MACCATALYST}" AND
+      "${LIB_OS}" MATCHES "^osx$")
+    # Build the macOS builtins with Mac Catalyst support.
+    list(APPEND builtin_cflags
+      -target ${LIB_ARCH}-apple-macos${DARWIN_osx_BUILTIN_MIN_VER}
+      -darwin-target-variant ${LIB_ARCH}-apple-ios13.1-macabi)
+  endif()
+
   set_target_compile_flags(${libname}
     ${sysroot_flag}
     ${DARWIN_${LIB_OS}_BUILTIN_MIN_VER_FLAG}
     ${builtin_cflags})
   target_include_directories(${libname}
     PRIVATE ${LIB_INCLUDE_DIRS})
   set_property(TARGET ${libname} APPEND PROPERTY
       COMPILE_DEFINITIONS ${LIB_DEFS})

compiler-rt/cmake/base-config-ix.cmake

 # The CompilerRT build system requires CMake version 2.8.8 or higher in order
 # to use its support for building convenience "libraries" as a collection of
 # .o files. This is particularly useful in producing larger, more complex
 # runtime libraries.
 
+include(BuiltinTests)
 include(CheckIncludeFile)
 include(CheckCXXSourceCompiles)
 include(GNUInstallDirs)
 include(ExtendPath)
 
 check_include_file(unwind.h HAVE_UNWIND_H)
 
 # Used by sanitizer_common and tests.
if(NOT EXISTS /usr/include/c++)
     else()
       message(STATUS "Found OSX_SYSROOT: ${OSX_SYSROOT}")
       set(OSX_SYSROOT_FLAG "-isysroot${OSX_SYSROOT}")
     endif()
   else()
     set(OSX_SYSROOT_FLAG "")
   endif()
 
+  try_compile_only(COMPILER_RT_HAS_DARWIN_TARGET_VARIANT_FLAG
+                   FLAGS
+                   "-target" "x86_64-apple-macos10.15"
+                   "-darwin-target-variant" "x86_64-apple-ios13.1-macabi"
+                   "-Werror")
+  option(COMPILER_RT_ENABLE_MACCATALYST "Enable building for Mac Catalyst" ${COMPILER_RT_HAS_DARWIN_TARGET_VARIANT_FLAG})
   option(COMPILER_RT_ENABLE_IOS "Enable building for iOS" On)
   option(COMPILER_RT_ENABLE_WATCHOS "Enable building for watchOS - Experimental" Off)
   option(COMPILER_RT_ENABLE_TVOS "Enable building for tvOS - Experimental" Off)
 
 else()
   option(COMPILER_RT_DEFAULT_TARGET_ONLY "Build builtins only for the default target" Off)
 endif()