Fix install_name in macOS using MACOS_RPATH

Instead of librst.1.dylib use @rpath/libsrt.1.dylib
This is also the recommended setting as per CMP0042 policy

CMakeLists.txt

@@ -304,9 +304,8 @@ if(WIN32)
 	message(STATUS "DETECTED SYSTEM: WINDOWS;  WIN32=1; PTW32_STATIC_LIB=1")
 	add_definitions(-DWIN32=1 -DPTW32_STATIC_LIB=1)
 elseif(DARWIN)
-	message(STATUS "DETECTED SYSTEM: DARWIN;  OSX=1; MACOSX_RPATH=OFF")
+	message(STATUS "DETECTED SYSTEM: DARWIN;  OSX=1")
 	add_definitions(-DOSX=1)
-	set(MACOSX_RPATH OFF)
 elseif(LINUX)
 	add_definitions(-DLINUX=1)
 	message(STATUS "DETECTED SYSTEM: LINUX;  LINUX=1" )
@@ -482,6 +481,8 @@ if (srt_libspec_shared)
 		target_link_libraries(${TARGET_srt}_shared PRIVATE ws2_32.lib)
 	elseif (MINGW)
 		target_link_libraries(${TARGET_srt}_shared PRIVATE wsock32.lib ws2_32.lib)
+	elseif (APPLE)
+		set_property(TARGET ${TARGET_srt}_shared PROPERTY MACOSX_RPATH ON)
 	endif()
 endif()