CMake: add option to link Swift content from Darwin toolchain

This is needed in specific Apple internal configurations -- as a result
of the limited applicability, this option is not exposed through
`build-script` on purpose.

Addresses rdar://127014753

Author: edymtt

CMakeLists.txt

@@ -532,6 +532,12 @@ set(SWIFT_DARWIN_STDLIB_INSTALL_NAME_DIR "/usr/lib/swift" CACHE STRING
 set(SWIFT_DARWIN_STDLIB_PRIVATE_INSTALL_NAME_DIR "@rpath" CACHE STRING
     "The directory of the install_name for the private standard library dylibs")
 
+option(SWIFT_ALLOW_LINKING_SWIFT_CONTENT_IN_DARWIN_TOOLCHAIN
+  "Adds search paths for libraries in the toolchain
+   when building Swift programs.
+   This is needed to support Apple internal configurations."
+  FALSE)
+
 set(SWIFT_DARWIN_DEPLOYMENT_VERSION_OSX "10.13" CACHE STRING
     "Minimum deployment target version for OS X")
 

cmake/modules/AddSwift.cmake

@@ -611,6 +611,11 @@ function(_add_swift_runtime_link_flags target relpath_to_lib_dir bootstrapping)
         endif()
       endif()
     endif()
+    if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS AND SWIFT_ALLOW_LINKING_SWIFT_CONTENT_IN_DARWIN_TOOLCHAIN)
+      get_filename_component(TOOLCHAIN_BIN_DIR ${SWIFT_EXEC_FOR_SWIFT_MODULES} DIRECTORY)
+      get_filename_component(TOOLCHAIN_LIB_DIR "${TOOLCHAIN_BIN_DIR}/../lib/swift/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}" ABSOLUTE)
+      target_link_directories(${target} BEFORE PUBLIC ${TOOLCHAIN_LIB_DIR})
+    endif()
     if(SWIFT_HOST_VARIANT_SDK MATCHES "LINUX|ANDROID|OPENBSD|FREEBSD" AND SWIFT_USE_LINKER STREQUAL "lld")
       target_link_options(${target} PRIVATE "SHELL:-Xlinker -z -Xlinker nostart-stop-gc")
     endif()

tools/SourceKit/cmake/modules/AddSwiftSourceKit.cmake

@@ -173,6 +173,12 @@ function(add_sourcekit_swift_runtime_link_flags target path HAS_SWIFT_MODULES)
         target_link_directories(${target} PUBLIC ${TOOLCHAIN_LIB_DIR})
       endif()
     endif()
+
+    if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_DARWIN_PLATFORMS AND SWIFT_ALLOW_LINKING_SWIFT_CONTENT_IN_DARWIN_TOOLCHAIN)
+      get_filename_component(TOOLCHAIN_BIN_DIR ${SWIFT_EXEC_FOR_SWIFT_MODULES} DIRECTORY)
+      get_filename_component(TOOLCHAIN_LIB_DIR "${TOOLCHAIN_BIN_DIR}/../lib/swift/${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_LIB_SUBDIR}" ABSOLUTE)
+      target_link_directories(${target} BEFORE PUBLIC ${TOOLCHAIN_LIB_DIR})
+    endif()
   endif()
 
   set(RPATH_LIST ${RPATH_LIST} PARENT_SCOPE)