[Tests] Add static keypaths module test.

Author: amritpan

build.sh

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+MODE=$1
+TEST=$2
+
+pushd ../build/${MODE}/swift-macosx-arm64
+xcrun ninja -j 8 swift-frontend
+#xcrun ninja -j 8 swift-refactor
+#xcrun ninja swift-demangle
+#xcrun ninja swift-serialize-diagnostics
+#xcrun ninja sil-opt
+#xcrun ninja swift-ide-test
+#xcrun ninja sourcekitd-test
+#xcrun ninja stdlib
+#xcrun ninja swift-remoteast
+popd
+python3 ../llvm-project/llvm/utils/lit/lit.py -sv --param swift_site_config=../build/${MODE}/swift-macosx-arm64/test-macosx-arm64/lit.site.cfg ${TEST}

test/ModuleInterface/static_keypaths_module.swift

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+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module -module-name Library \
+// RUN:     -swift-version 5 -enable-library-evolution \
+// RUN:     -o %t/Library.swiftmodule \
+// RUN:     -emit-module-interface-path %t/Library.swiftinterface \
+// RUN:     %t/Library.swift
+
+/// Verify that we can build from the Library.swiftmodule
+// RUN: %target-swift-frontend -typecheck -module-name Client \
+// RUN:     -swift-version 5 \
+// RUN:     %t/Client.swift -I%t
+
+/// Verify what we can build from a swiftinterface, when swiftmodule was deleted
+// RUN: rm %t/Library.swiftmodule
+// RUN: %target-swift-frontend -typecheck -module-name Client \
+// RUN:     -swift-version 5 \
+// RUN:     %t/Client.swift -I%t
+
+// REQUIRES: executable_test
+
+//--- Library.swift
+public struct AStruct {
+  public static var property1: Int = 1
+  private(set) public static var property2: Int = 4
+  private(set) public static var property3: Int = 4
+}
+
+//--- Client.swift
+import Library
+
+public let keyPath1 = \AStruct.Type.property1
+public let keyPath2 = \AStruct.Type.property2
+public let keyPath3 = \AStruct.Type.property3
+
+// CHECK: false
+print(keyPath1 == keyPath2)
+
+// CHECK: true
+print(keyPath2 == keyPath3)
+