[CMake] Support externalizing debug info on Darwin

* Adds COMPILER_RT_EXTERNALIZE_DEBUGINFO option
* On Darwin this results in calling dsymutil and strip after linking
* This generates an error on non-darwin platforms, matching the LLVM behavior

llvm-svn: 254643
diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
index 9b6b2ea..5f8b4d1 100644
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -189,6 +189,8 @@
 endif()
 
 option(COMPILER_RT_DEBUG "Build runtimes with full debug info" OFF)
+option(COMPILER_RT_EXTERNALIZE_DEBUGINFO
+  "Generate dSYM files and strip executables and libraries (Darwin Only)" OFF)
 # COMPILER_RT_DEBUG_PYBOOL is used by lit.common.configured.in.
 pythonize_bool(COMPILER_RT_DEBUG)