[test] Move BlocksRuntimeStubs into its own folder under stdlib/.

BlocksRuntimeStubs is built for the target SDK(s), but it was using one
of the stdlib CMake helpers without setting up the same environment as
the stdlib/ folder is setting.

To avoid problems, like BlocksRuntimeStubs being built with the host
compiler, instead of the just built compiler, and other difficult to
understand problems, create a folder for it in stdlib/private/. This
will allow the usage of the stdlib CMake function in the same environment
that is normally used.

Author: drodriguez

stdlib/private/BlocksRuntimeStubs/BlocksRuntime.c

@@ -0,0 +1,6 @@
+void
+#if defined(_WIN32)
+__declspec(dllexport)
+#endif
+_Block_release(void) {  }
+

stdlib/private/BlocksRuntimeStubs/CMakeLists.txt

@@ -0,0 +1,31 @@
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/../../../test/cmake/modules")
+
+include(SwiftTestUtils)
+
+foreach(SDK ${SWIFT_SDKS})
+  foreach(ARCH ${SWIFT_SDK_${SDK}_ARCHITECTURES})
+    get_swift_test_build_flavors(build_flavors "${SDK}")
+
+    foreach(BUILD_FLAVOR build_flavors)
+      get_swift_test_variant_suffix(VARIANT_SUFFIX "${SDK}" "${ARCH}" "${BUILD_FLAVOR}")
+
+      set(test_bin_dir "${CMAKE_BINARY_DIR}/test${VARIANT_SUFFIX}")
+
+      _add_swift_target_library_single(
+        BlocksRuntimeStub${VARIANT_SUFFIX}
+        BlocksRuntimeStub
+        SHARED
+        ARCHITECTURE ${ARCH}
+        SDK ${SDK}
+        INSTALL_IN_COMPONENT dev
+        BlocksRuntime.c
+      )
+      set_target_properties(BlocksRuntimeStub${VARIANT_SUFFIX} PROPERTIES
+        ARCHIVE_OUTPUT_DIRECTORY ${test_bin_dir}
+        LIBRARY_OUTPUT_DIRECTORY ${test_bin_dir}
+        RUNTIME_OUTPUT_DIRECTORY ${test_bin_dir}
+        OUTPUT_NAME BlocksRuntime)
+    endforeach()
+  endforeach()
+endforeach()
+

stdlib/private/CMakeLists.txt

@@ -29,9 +29,18 @@ if(SWIFT_BUILD_SDK_OVERLAY)
   if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
     add_subdirectory(StdlibUnittestFoundationExtras)
   endif()
-  # Currently SwiftReflectionTest cannot be built on Windows, due to 
-  # dependencies on POSIX symbols 
+  # Currently SwiftReflectionTest cannot be built on Windows, due to
+  # dependencies on POSIX symbols
   if (SWIFT_INCLUDE_TESTS AND (NOT CMAKE_SYSTEM_NAME STREQUAL "Windows"))
     add_subdirectory(SwiftReflectionTest)
   endif()
 endif()
+
+# Keep in sync with stdlib/tools/CMakeLists.txt: swift-reflection-test is
+# only used when testing dynamic stdlib.
+if(SWIFT_BUILD_DYNAMIC_STDLIB AND SWIFT_INCLUDE_TESTS)
+  # NOTE create a stub BlocksRuntime library that can be used for the
+  # reflection tests
+  add_subdirectory(BlocksRuntimeStubs)
+endif()
+

test/CMakeLists.txt

@@ -249,27 +249,6 @@ foreach(SDK ${SWIFT_SDKS})
     # Keep in sync with stdlib/tools/CMakeLists.txt: swift-reflection-test is
     # only used when testing dynamic stdlib.
     if(SWIFT_BUILD_DYNAMIC_STDLIB AND SWIFT_INCLUDE_TESTS)
-      # NOTE create a stub BlocksRuntime library that can be used for the
-      # reflection tests
-      file(WRITE ${test_bin_dir}/Inputs/BlocksRuntime.c
-        "void
-#if defined(_WIN32)
-__declspec(dllexport)
-#endif
-_Block_release(void) { }\n")
-      _add_swift_target_library_single(
-        BlocksRuntimeStub${VARIANT_SUFFIX}
-        BlocksRuntimeStub
-        SHARED
-        ARCHITECTURE ${ARCH}
-        SDK ${SDK}
-        INSTALL_IN_COMPONENT dev
-        ${test_bin_dir}/Inputs/BlocksRuntime.c)
-      set_target_properties(BlocksRuntimeStub${VARIANT_SUFFIX} PROPERTIES
-        ARCHIVE_OUTPUT_DIRECTORY ${test_bin_dir}
-        LIBRARY_OUTPUT_DIRECTORY ${test_bin_dir}
-        RUNTIME_OUTPUT_DIRECTORY ${test_bin_dir}
-        OUTPUT_NAME BlocksRuntime)
       list(APPEND test_dependencies BlocksRuntimeStub${VARIANT_SUFFIX})
 
       list(APPEND test_dependencies