Do not test inferior Swift libraries on Darwin

On platforms with ABI-stable Swift runtime libraries (currently only Darwin), we should not set `DYLD_LIBRARY_PATHS` to include the inferior Swift libs in `bootstrap` because compatibility issues can arise from SwiftPM's use of Foundation (which itself is a client of the stdlib) and from using dyld4 (which is used on macOS 12+).

rdar://88475529

Author: neonichu

Utilities/bootstrap

@@ -684,7 +684,7 @@ def get_swiftpm_env_cmd(args):
     env_cmd.append("SWIFTPM_MACOS_DEPLOYMENT_TARGET=%s" % g_macos_deployment_target)
 
     if args.bootstrap:
-        libs_joined = ":".join([
+        library_paths = [
             os.path.join(args.bootstrap_dir,                       "lib"),
             os.path.join(args.build_dirs["tsc"],                   "lib"),
             os.path.join(args.build_dirs["llbuild"],               "lib"),
@@ -694,11 +694,17 @@ def get_swiftpm_env_cmd(args):
             os.path.join(args.build_dirs["swift-crypto"],          "lib"),
             os.path.join(args.build_dirs["swift-system"],          "lib"),
             os.path.join(args.build_dirs["swift-collections"],     "lib"),
-        ] + args.target_info["paths"]["runtimeLibraryPaths"])
+        ]
 
         if platform.system() == 'Darwin':
+            # Need to include backwards compatibility libraries for Concurrency
+            # FIXME: Would be nice if we could get this from `swiftc -print-target-info`
+            back_compat = args.target_info["paths"]["runtimeLibraryPaths"][0] + '../../swift-5.5/macosx'
+            # Does not include Swift runtime library paths because of rdar://75752698
+            libs_joined = ":".join(library_paths + [back_compat])
             env_cmd.append("DYLD_LIBRARY_PATH=%s" % libs_joined)
         else:
+            libs_joined = ":".join(library_paths + args.target_info["paths"]["runtimeLibraryPaths"])
             env_cmd.append("LD_LIBRARY_PATH=%s" % libs_joined)
 
     return env_cmd