[cmake] Copy Dispatch to the SDK subdir on host.

We have two directories for Swift libraries,
* `SWIFT_SDK_<platform>_LIB_SUBDIR`, a.k.a., the SDK subdir,
  a.k.a., `swift-<platform>-<arch>/lib/swift/<platform>`, and
* `SWIFTLIB_SINGLE_SUBDIR`,
  a.k.a., `swift-<platform>-<arch>/lib/swift/<platform>/<arch>`.

Through the Swift build, libraries are emitted to both
`.../lib/swift/<platform>` and `.../lib/swift/<platform>/<arch>`.
However, when building toolchains, only `.../lib/swift/<platform>/` is
populated with libraries.

None of this normally isn't a problem; the Swift libraries do not have
inherent interdependencies. This however changes with Concurrency:
Concurrency has an implicit dependency on libdispatch.

When Swift is built, we have two copies of `libswift_Concurrency.so`:
one in `.../lib/swift/<platform>` and one in
`.../lib/swift/<platform>/<arch>`. Prior to this commit, we
unconditionally copy `libdispatch.so` and `libBlocksRuntime.so` to only
_one_ place -- that is, `.../lib/swift/<platform>/<arch>`.

swiftc emits binaries on ELF systems with an rpath of
`.../lib/swift/<platform>`. These binaries implicitly import
Concurrency, so they link against `libswift_Concurrency.so` (whether
they use Concurrency features or not). The library's `$ORIGIN` is
searched to find `libdispatch.so`.

Now, nothing breaks on Linux because there the loader, when given an
rpath, searches both `.../lib/swift/<platform>` and
`.../lib/swift/<platform>/<arch>` even though the rpath only specifies
one directory..

However, on other platforms, only the given rpath is searched.
`libdispatch.so` does not reside next to `libswift_Concurrency.so`
because it has been copied to  `.../lib/swift/<platform>/<arch>`; not in
the rpath.

There are a few ways to solve this: change the way rpaths are
configured, only emit libraries into one place, copy `libdispatch.so`
only to the path matching the rpath, or copy `libdispatch.so` wherever
`libswift_Concurrency.so` is copied,

Because the toolchain file layout is different to the file layout when
only Swift is built, hacking the rpath is brittle. Presumably, the
reason why we have a `libswift_Concurrency.so` residing in two places is
to support builds where multiple architectures are supported in the one
build directory, so we cannot just copy `libdispatch.so` _only_ to
`.../lib/swift/<platform>`.

Ultimately, We need to ensure that every instance where
`libswift_Concurrency.so` can be used has `libdispatch.so` residing next
to it, which we do here.

Note that this implicit dependency resolution would not happen unless we
added a `-ldispatch` flag to make this all work, but other platforms are
instaed using `$ORIGIN` to get the search to work properly, so we also
do this for OpenBSD in this commit.

Author: 3405691582

cmake/modules/Libdispatch.cmake

@@ -110,6 +110,14 @@ foreach(sdk ${DISPATCH_SDKS})
                           ${CMAKE_COMMAND} -E copy
                           <INSTALL_DIR>/${LIBDISPATCH_RUNTIME_DIR}/${SWIFT_SDK_${sdk}_SHARED_LIBRARY_PREFIX}BlocksRuntime${SWIFT_SDK_${sdk}_SHARED_LIBRARY_SUFFIX}
                           ${SWIFTLIB_DIR}/${SWIFT_SDK_${sdk}_LIB_SUBDIR}/${arch}/${SWIFT_SDK_${sdk}_SHARED_LIBRARY_PREFIX}BlocksRuntime${SWIFT_SDK_${sdk}_SHARED_LIBRARY_SUFFIX}
+                        COMMAND
+                          ${CMAKE_COMMAND} -E copy
+                          <INSTALL_DIR>/${LIBDISPATCH_RUNTIME_DIR}/${SWIFT_SDK_${sdk}_SHARED_LIBRARY_PREFIX}dispatch${SWIFT_SDK_${sdk}_SHARED_LIBRARY_SUFFIX}
+                          ${SWIFTLIB_DIR}/${SWIFT_SDK_${sdk}_LIB_SUBDIR}/${SWIFT_SDK_${sdk}_SHARED_LIBRARY_PREFIX}dispatch${SWIFT_SDK_${sdk}_SHARED_LIBRARY_SUFFIX}
+                        COMMAND
+			  ${CMAKE_COMMAND} -E copy
+                          <INSTALL_DIR>/${LIBDISPATCH_RUNTIME_DIR}/${SWIFT_SDK_${sdk}_SHARED_LIBRARY_PREFIX}BlocksRuntime${SWIFT_SDK_${sdk}_SHARED_LIBRARY_SUFFIX}
+                          ${SWIFTLIB_DIR}/${SWIFT_SDK_${sdk}_LIB_SUBDIR}/${SWIFT_SDK_${sdk}_SHARED_LIBRARY_PREFIX}BlocksRuntime${SWIFT_SDK_${sdk}_SHARED_LIBRARY_SUFFIX}
                         STEP_TARGETS
                           install
                         BUILD_BYPRODUCTS

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -995,6 +995,10 @@ function(_add_swift_target_library_single target name)
         PROPERTIES
         INSTALL_RPATH "$ORIGIN")
     endif()
+  elseif("${SWIFTLIB_SINGLE_SDK}" STREQUAL "OPENBSD")
+    set_target_properties("${target}"
+      PROPERTIES
+      INSTALL_RPATH "$ORIGIN")
   endif()
 
   set_target_properties("${target}" PROPERTIES BUILD_WITH_INSTALL_RPATH YES)