[cmake] Support LLD for CLANG_ORDER_FILE

[smeenai]

Summary

LLD also supports order files using the --symbol-ordering-file option.
As the name would suggest, the order file format is slightly different
from gold; gold's order files specify section names, whereas LLD's
specify symbol names. Assuming you have an order file in the correct
format though, we should support using it with LLD.

Switch the check to actually use LLVM's linker detection rather than
just checking for the presence of the gold executable, since we might
have a gold executable present but be using LLD (or bfd for that matter)
as our linker.

[phosek]

LGTM

[ruiu]

LGTM

cfe/trunk/tools/driver/CMakeLists.txt

if (APPLE)
   configure_file("${TOOL_INFO_PLIST}.in" "${TOOL_INFO_PLIST_OUT}" @ONLY)
 
   set(TOOL_INFO_UTI)
   set(TOOL_INFO_NAME)
   set(TOOL_INFO_VERSION)
   set(TOOL_INFO_BUILD_VERSION)
 endif()
 
-if(CLANG_ORDER_FILE AND (LD64_EXECUTABLE OR GOLD_EXECUTABLE))
+if(CLANG_ORDER_FILE AND
+   (LD64_EXECUTABLE OR LLVM_LINKER_IS_GOLD OR LLVM_LINKER_IS_LLD))
   include(CheckLinkerFlag)
 
   if (LD64_EXECUTABLE)
     set(LINKER_ORDER_FILE_OPTION "-Wl,-order_file,${CLANG_ORDER_FILE}")
-  elseif (GOLD_EXECUTABLE)
+  elseif (LLVM_LINKER_IS_GOLD)
     set(LINKER_ORDER_FILE_OPTION "-Wl,--section-ordering-file,${CLANG_ORDER_FILE}")
+  elseif (LLVM_LINKER_IS_LLD)
+    set(LINKER_ORDER_FILE_OPTION "-Wl,--symbol-ordering-file,${CLANG_ORDER_FILE}")
   endif()
 
   # This is a test to ensure the actual order file works with the linker.
   check_linker_flag(${LINKER_ORDER_FILE_OPTION} LINKER_ORDER_FILE_WORKS)
 
   # Passing an empty order file disables some linker layout optimizations.
   # To work around this and enable workflows for re-linking when the order file
   # changes we check during configuration if the file is empty, and make it a