Split swift-refleciton-test into host and target test targets

swift-reflection-test is now the test that forks a swift executable
and performs remote reflection, making it runnable on other targets,
such as the iOS simulator.

swift-reflection-dump is now a host-side tool that dumps the remote
reflection sections for any platform binary and will continue to
link in LLVM object file support.

This necessitates finally moving lib/Refleciton into stdlib/public,
since we're linking target-specific versions of the test tool and
we would eventually like to adopt some of this functionality in
the runtime anyway.

include/swift/Reflection/Reader.h

@@ -22,6 +22,7 @@
 
 #include <dlfcn.h>
 #include <cstdint>
+#include <cstring>
 #include <memory>
 #include <vector>