Break link against compiler-rt

This patch replaces the platform version check with a dlsym to grab the
symbol we need. If we're on a new enough platform, the symbol should be
available and we can use it. Otherwise, it will be empty and we should
return true. This breaks the link requirement for the platform version
symbol.

Author: etcwilde

stdlib/toolchain/Compatibility56/include/Concurrency/VoucherShims.h

@@ -20,6 +20,9 @@
 #include <cstdint>
 #include "swift/Runtime/Config.h"
 
+#include "swift/Basic/Lazy.h"
+#include <dlfcn.h>
+
 // swift-corelibs-libdispatch has os/voucher_private.h but it doesn't work for
 // us yet, so only look for it on Apple platforms.
 #if __APPLE__ && __has_include(<os/voucher_private.h>)
@@ -42,7 +45,7 @@
 
 #if SWIFT_HAS_VOUCHER_HEADER
 
-#else
+#else // SWIFT_HAS_VOUCHER_HEADER
 
 // If the header isn't available, declare the necessary calls here.
 
@@ -92,8 +95,14 @@ static inline bool voucher_needs_adopt(void * _Nullable voucher) {
 
 static inline bool swift_voucher_needs_adopt(voucher_t _Nullable voucher) {
 #if __APPLE__
-  if (__builtin_available(macOS 12.0, iOS 15.0, tvOS 15.0, watchOS 8.0, *))
-    return voucher_needs_adopt(voucher);
+  // _Z19voucher_needs_adoptP9voucher_s
+  const auto voucherNeedsAdopt =
+      reinterpret_cast<bool(*)(voucher_t)>(SWIFT_LAZY_CONSTANT(
+          dlsym(RTLD_DEFAULT, "_Z19voucher_needs_adoptP9voucher_s")));
+
+  if (voucherNeedsAdopt) {
+    return voucherNeedsAdopt(voucher);
+  }
   return true;
 #else
   return voucher_needs_adopt(voucher);