[Backtracing][Tests] Fix the name of the swift-backtrace dependency.

Because it's a target executable, the name of the dependency is suffixed
with the SDK.

rdar://124913332

Author: al45tair

Diff for: test/CMakeLists.txt

@@ -82,9 +82,9 @@ function(get_test_dependencies SDK result_var_name)
 
   set(deps_binaries)
 
-  if (SWIFT_ENABLE_BACKTRACING)
+  if (SWIFT_BUILD_LIBEXEC AND SWIFT_ENABLE_BACKTRACING)
     list(APPEND deps_binaries
-      swift-backtrace)
+      "swift-backtrace-${SDK}")
   endif()
 
   if (SWIFT_INCLUDE_TOOLS)