Enable BUILD_LIBRARY_FOR_DISTRIBUTION

Originally requested by @dive in #1110.

This should remain on a separate branch for now. For more information see #1110.

Configs/Module-Shared.xcconfig

@@ -7,6 +7,10 @@ ALLOW_TARGET_PLATFORM_SPECIALIZATION = YES
 // This setting is deprecated as of Xcode 8.3 and may not be supported in future versions. It is recommended that you disable the setting. If enabled, both `#include <header.h>`-style and `#include "header.h"`-style directives search the paths in `USER_HEADER_SEARCH_PATHS` before `HEADER_SEARCH_PATHS`
 ALWAYS_SEARCH_USER_PATHS = NO
 
+// !!!: EXPERIMENTAL
+// Ensures that your libraries are built for distribution. For Swift, this enables support for library evolution and generation of a module interface file.
+BUILD_LIBRARY_FOR_DISTRIBUTION = YES
+
 // Warn when using non-localized strings.
 CLANG_ANALYZER_LOCALIZABILITY_NONLOCALIZED = YES;