Use --dsym-dir when compiling with a compiler that supports it

[dsanders]

Summary

As part of this, a couple tweaks to --dsym-dir have been made. It now starts
with a double dash since CMake is unable to detect it's availability otherwise.
clang's that lack it ended up passing the check anyway because of the -d group
accepting anything. Also added the --dsym-dir= variant as the behaviour of
Joined surprised me by including the = in the value otherwise.

clang/include/clang/Driver/Options.td

def dM : Flag<["-"], "dM">, Group<d_Group>, Flags<[CC1Option]>,
   HelpText<"Print macro definitions in -E mode instead of normal output">;
 def dead__strip : Flag<["-"], "dead_strip">;
 def dependency_file : Separate<["-"], "dependency-file">, Flags<[CC1Option]>,
   HelpText<"Filename (or -) to write dependency output to">;
 def dependency_dot : Separate<["-"], "dependency-dot">, Flags<[CC1Option]>,
   HelpText<"Filename to write DOT-formatted header dependencies to">;
 def module_dependency_dir : Separate<["-"], "module-dependency-dir">,
   Flags<[CC1Option]>, HelpText<"Directory to dump module dependencies to">;
-def dsym_dir : JoinedOrSeparate<["-"], "dsym-dir">,
+def dsym_dir : Separate<["--"], "dsym-dir">,
   Flags<[DriverOption, RenderAsInput]>,
   HelpText<"Directory to output dSYM's (if any) to">, MetaVarName<"<dir>">;
+def dsym_dir_EQ : Joined<["--"], "dsym-dir=">, Alias<dsym_dir>;
 def dumpmachine : Flag<["-"], "dumpmachine">;
 def dumpspecs : Flag<["-"], "dumpspecs">, Flags<[Unsupported]>;
 def dumpversion : Flag<["-"], "dumpversion">;
 def dylib__file : Separate<["-"], "dylib_file">;
 def dylinker__install__name : JoinedOrSeparate<["-"], "dylinker_install_name">;
 def dylinker : Flag<["-"], "dylinker">;
 def dynamiclib : Flag<["-"], "dynamiclib">;
 def dynamic : Flag<["-"], "dynamic">, Flags<[NoArgumentUnused]>;

clang/test/Driver/darwin-dsymutil.c

 // RUN:          -check-prefix=CHECK-OUTPUT-NAME < %t %s
 //
 // RUN: %clang -target x86_64-apple-darwin10 -ccc-print-bindings \
 // RUN:   -o bar/foo %s -g 2> %t
 // RUN: FileCheck -Doutfile=bar/foo -Ddsymfile=bar/foo.dSYM \
 // RUN:           -check-prefix=CHECK-OUTPUT-NAME < %t %s
 //
 // RUN: %clang -target x86_64-apple-darwin10 -ccc-print-bindings \
-// RUN:   -o bar/foo -dsym-dir external %s -g 2> %t
+// RUN:   -o bar/foo --dsym-dir external %s -g 2> %t
 // RUN: FileCheck -Doutfile=bar/foo -Ddsymfile=external/foo.dSYM \
 // RUN:           -check-prefix=CHECK-OUTPUT-NAME < %t %s
 //
 // CHECK-OUTPUT-NAME: "x86_64-apple-darwin10" - "darwin::Linker", inputs: [{{.*}}], output: "[[outfile]]"
 // CHECK-OUTPUT-NAME: "x86_64-apple-darwin10" - "darwin::Dsymutil", inputs: ["[[outfile]]"], output: "[[dsymfile]]"
 
 // Check that we only use dsymutil when needed.
 //
 // RUN: touch %t.o
 // RUN: %clang -target x86_64-apple-darwin10 -ccc-print-bindings \
 // RUN:   -o foo %t.o -g 2> %t
 // RUN: not grep "Dsymutil" %t
 
 // Check that we don't crash when translating arguments for dsymutil.
 // RUN: %clang -m32 -arch x86_64 -g %s -###

llvm/cmake/modules/AddLLVM.cmake

if(APPLE)
     # linked. See https://bugs.llvm.org/show_bug.cgi?id=46841 for more
     # information.
     set(empty_src
         ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR}/${name}-empty.cpp)
     file(WRITE "${empty_src}" "extern int dummy;\n")
     set_property(TARGET ${name} APPEND_STRING PROPERTY
       LINK_FLAGS " ${empty_src}")
     if(LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR)
+      check_cxx_compiler_flag("--dsym-dir=foo" HAS_DSYM_DIR)
+      if (HAS_DSYM_DIR)
+        set_property(TARGET ${name} APPEND_STRING PROPERTY
+                     LINK_FLAGS " --dsym-dir=${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}")
+        add_custom_command(TARGET ${name} PRE_BUILD
+          COMMAND ${CMAKE_COMMAND} -E make_directory "${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}")
+      else()
         # clang can currently only emit dSYM's to the same directory as the output
         # binary. Workaround this by moving it after the build.
         set(output_name "$<TARGET_FILE_NAME:${name}>.${file_ext}")
         set(output_path "${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}/${output_name}")
         add_custom_command(TARGET ${name} POST_BUILD
           COMMAND ${CMAKE_COMMAND} -E make_directory "${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}"
           # Remove any old versions if present
           COMMAND ${CMAKE_COMMAND} -E rm "-rf" "${output_path}"
           # Move the dSYM clang emitted next to the output binary where we want it
           # to be.
           COMMAND ${CMAKE_COMMAND}
                       -DFROM="$<TARGET_FILE:${name}>.${file_ext}"
                       -DTO="${output_path}"
                       -P ${LLVM_CMAKE_PATH}/MoveIfExists.cmake
         )
       endif()
+    endif()
     add_custom_command(TARGET ${name} POST_BUILD
       COMMAND ${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}>