[CMake] Add LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR for custom dSYM target directory on Darwin

[sgraenitz]

Summary

When using LLVM_EXTERNALIZE_DEBUGINFO in LLDB, the default dSYM location for the shared library in LLDB.framework is inside the framework bundle. With LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR we can easily fix that. I consider it a useful feature to be able to set a global output directory for external debug info (rather then having a target-specific one). Only implemented for Darwin so far.

[aprantl]

Looks reasonable, thanks!

cmake/modules/AddLLVM.cmake

if(APPLE)
         set(CMAKE_STRIP xcrun strip)
       endif()
       set(strip_command COMMAND ${CMAKE_STRIP} -Sxl $<TARGET_FILE:${name}>)
     else()
       set(strip_command COMMAND ${CMAKE_STRIP} -g -x $<TARGET_FILE:${name}>)
     endif()
   endif()
 
+  if(LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR)
+    if(APPLE)
+      set(output_name "$<TARGET_FILE_NAME:${name}>.dSYM")
+      set(output_path "-o=${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}/${output_name}")
+    endif()
+  endif()
+
   if(APPLE)
     if(CMAKE_CXX_FLAGS MATCHES "-flto"
       OR CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE} MATCHES "-flto")
 
       set(lto_object ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR}/${name}-lto.o)
       set_property(TARGET ${name} APPEND_STRING PROPERTY
         LINK_FLAGS " -Wl,-object_path_lto,${lto_object}")
     endif()
     if(NOT CMAKE_DSYMUTIL)
       set(CMAKE_DSYMUTIL xcrun dsymutil)
     endif()
     add_custom_command(TARGET ${name} POST_BUILD
-      COMMAND ${CMAKE_DSYMUTIL} $<TARGET_FILE:${name}>
+      COMMAND ${CMAKE_DSYMUTIL} ${output_path} $<TARGET_FILE:${name}>
       ${strip_command}
       )
   else()
     add_custom_command(TARGET ${name} POST_BUILD
       COMMAND ${CMAKE_OBJCOPY} --only-keep-debug $<TARGET_FILE:${name}> $<TARGET_FILE:${name}>.debug
       ${strip_command} -R .gnu_debuglink
       COMMAND ${CMAKE_OBJCOPY} --add-gnu-debuglink=$<TARGET_FILE:${name}>.debug $<TARGET_FILE:${name}>
       )