runtime: fix the long test build on Windows

The standard library stubs need to be built with swiftCore_EXPORTS
defined to ensure that the interfaces are exported as if the swiftCore
library was being built.  This allows building the LongTests on Windows.

Author: compnerd

unittests/runtime/LongTests/CMakeLists.txt

@@ -38,6 +38,14 @@ if(("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "${SWIFT_PRIMARY_VARIANT_SDK}") AND
     $<TARGET_OBJECTS:swiftRuntime${SWIFT_PRIMARY_VARIANT_SUFFIX}>
     )
 
+  # The local stdlib implementation provides definitions of the swiftCore
+  # interfaes to avoid pulling in swiftCore itself.  Build the
+  # SwiftRuntimeLongTests with swiftCore_EXPORTS to permit exporting the stdlib
+  # interfaces.
+  target_compile_definitions(SwiftRuntimeLongTests
+                             PRIVATE
+                               swiftCore_EXPORTS)
+
   # FIXME: cross-compile for all variants.
   target_link_libraries(SwiftRuntimeLongTests
     swiftCore${SWIFT_PRIMARY_VARIANT_SUFFIX}