Specifying `-platform_version` targeting macos before 10.15 causes cctools ld
to link with `@rpath`. This may have something to do with Swift ABI stability.

--- a/products/llbuildSwift/CMakeLists.txt
+++ b/products/llbuildSwift/CMakeLists.txt
@@ -22,7 +17,7 @@ endif()

 # TODO(compnerd) move both of these outside of the CMake into the invocation
 if(CMAKE_SYSTEM_NAME STREQUAL Darwin)
-  add_compile_options(-target ${CMAKE_OSX_ARCHITECTURES}-apple-macosx10.10)
+  add_compile_options(-target ${CMAKE_OSX_ARCHITECTURES}-apple-macosx10.15)
   if(NOT CMAKE_OSX_SYSROOT STREQUAL "")
     add_compile_options(-sdk ${CMAKE_OSX_SYSROOT})
   endif()