build: simplify check using the SDK OBJECT_FORMAT

_OBJECT_FORMAT was added recentlyish for all the SDKs.  Use that property rather
than enumerating all the ELFish targets.  This ensures that the code path is
correct if another ELFish target is ported to.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -578,20 +578,16 @@ function(_add_swift_library_single target name)
     set(SWIFTLIB_SINGLE_API_NOTES "${module_name}")
   endif()
 
-  # On platforms that use ELF binaries (for now that is Linux and FreeBSD)
-  # we add markers for metadata sections in the shared libraries using 
-  # these object files.  This wouldn't be necessary if the link was done by
-  # the swift binary: rdar://problem/19007002
-  if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "LINUX" OR
-     "${SWIFTLIB_SINGLE_SDK}" STREQUAL "FREEBSD")
-
+  # On platforms that use ELF binaries we add markers for metadata sections in
+  # the shared libraries using these object files.  This wouldn't be necessary
+  # if the link was done by the swift binary: rdar://problem/19007002
+  if("${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_OBJECT_FORMAT}" STREQUAL "ELF")
     if("${libkind}" STREQUAL "SHARED")
       set(arch_subdir "${SWIFTLIB_DIR}/${SWIFTLIB_SINGLE_SUBDIR}")
 
       set(SWIFT_SECTIONS_OBJECT_BEGIN "${arch_subdir}/swift_begin.o")
       set(SWIFT_SECTIONS_OBJECT_END   "${arch_subdir}/swift_end.o")
     endif()
-
   endif()
 
   # FIXME: don't actually depend on the libraries in SWIFTLIB_SINGLE_LINK_LIBRARIES,