Update test to link against the Darwin SDK

Author: DougGregor

test/DebugInfo/ASTSection_linker.swift

@@ -2,22 +2,22 @@
 
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend -c -sdk /fake/sdk/path -Xcc -DA -Xcc -DB -emit-module -o %t %S/ASTSection.swift -swift-version 4
+// RUN: %target-swift-frontend -c -Xcc -DA -Xcc -DB -emit-module -o %t %S/ASTSection.swift -swift-version 4
 // RUN: %swift-ide-test -test-CompilerInvocation-from-module -source-filename=%t/ASTSection.swiftmodule
 
 // Test the inline section mechanism.
-// RUN: %target-ld %t/ASTSection.o -sectcreate __DWARF __swift_ast %t/ASTSection.swiftmodule -o %t/ASTSection.dylib -dylib -lSystem -lobjc
+// RUN: %target-ld %t/ASTSection.o -sectcreate __DWARF __swift_ast %t/ASTSection.swiftmodule -o %t/ASTSection.dylib -dylib -L%sdk/usr/lib -lSystem -lobjc
 // RUN: %lldb-moduleimport-test -verbose %t/ASTSection.dylib | %FileCheck %s
 
 // Test the symbol table entry.
-// RUN: %target-ld %t/ASTSection.o -add_ast_path %t/ASTSection.swiftmodule -o %t/ASTSection.dylib -dylib -lSystem -lobjc
+// RUN: %target-ld %t/ASTSection.o -add_ast_path %t/ASTSection.swiftmodule -o %t/ASTSection.dylib -dylib -L%sdk/usr/lib -lSystem -lobjc
 // RUN: %lldb-moduleimport-test -verbose %t/ASTSection.dylib | %FileCheck %s
 
 // REQUIRES: OS=macosx
 
 // CHECK: - Swift Version: {{.+}}.{{.+}}
 // CHECK: - Compatibility Version: 4
 // CHECK: - Target: {{.+}}-{{.+}}-{{.+}}
-// CHECK: - SDK path: /fake/sdk/path{{$}}
+// CHECK: - SDK path: {{.*}}MacOS{{.*}}.sdk
 // CHECK: - -Xcc options: -working-directory {{.+}} -DA -DB
 // CHECK: Importing ASTSection... ok!