[test] One last tweak to "%target-run-reflection-test"

Copy %target-swift-reflection-test into %t instead of using a hard
link. The problem with hard links is that they can be overwritten when
the test fails, which would then truncate the original executable to
an empty file!

Author: jrose-apple

validation-test/Reflection/lit.local.cfg

@@ -2,9 +2,9 @@
 config.substitutions = list(config.substitutions)
 
 config.substitutions.insert(0, ("%target-run-reflection-test",
-    # Link %target-swift-reflection-test into %t to convince %target-run to copy
+    # Copy %target-swift-reflection-test into %t to convince %target-run to copy
     # it, then use DYLD_LIBRARY_PATH to make sure it can find SwiftRemoteMirrors
     # from its new location when /not/ run remotely.
-    ("ln %target-swift-reflection-test %t/swift-reflection-test && "
+    ("cp %target-swift-reflection-test %t/swift-reflection-test && "
         "env %env-DYLD_LIBRARY_PATH=%platform-module-dir/../ %target-run "
         " %t/swift-reflection-test")))