Use the SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT macro guard in magic-symbols-for-install-name.c (swiftlang#41280)

Author: kubamracek

stdlib/linker-support/magic-symbols-for-install-name.c

@@ -89,4 +89,4 @@
   #error Unknown target.
 #endif
 
-#endif // defined(__APPLE__) && defined(__MACH__)
+#endif // defined(__APPLE__) && defined(__MACH__) && SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT

stdlib/public/Concurrency/linker-support/magic-symbols-for-install-name.c

@@ -20,7 +20,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if defined(__APPLE__) && defined(__MACH__)
+#if defined(__APPLE__) && defined(__MACH__) && SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT
 
 #include <Availability.h>
 #include <TargetConditionals.h>
@@ -134,4 +134,4 @@ const char ld_previous_macCatalyst = 0;
   #error Unknown target.
 #endif
 
-#endif // defined(__APPLE__) && defined(__MACH__)
+#endif // defined(__APPLE__) && defined(__MACH__) && SWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT