CMake: on Darwin be explicit about inclusion in the dyld shared cache

This entails passing a linker flags when the standard library is not
meant for inclusion in such cache -- such flag is supported by both LLD
and the Apple linkers.

For this to have effect on every library, propagate link flags when
building _Concurrency and Observation.

This is needed for Apple internal configurations.

Addresses rdar://120653968

Author: edymtt

stdlib/public/CMakeLists.txt

@@ -19,6 +19,20 @@ if(SWIFT_STDLIB_SIL_DEBUGGING)
   list(APPEND SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS "-Xfrontend" "-sil-based-debuginfo")
 endif()
 
+option(SWIFT_RUNTIME_PART_OF_DARWIN_SHARED_CACHE
+       "On Darwin platforms, link the standard library in a way that
+       allows inclusion in the dyld shared cache"
+       FALSE)
+
+if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+    set(linker_detected "$<BOOL:${LLVM_LINKER_DETECTED}>")
+    set(runtime_not_in_shared_cache "$<NOT:$<BOOL:${SWIFT_RUNTIME_PART_OF_DARWIN_SHARED_CACHE}>>")
+    set(shared_cache_link_flags
+      "$<$<AND:${linker_detected},${runtime_not_in_shared_cache}>:LINKER:-not_for_dyld_shared_cache>")
+    list(APPEND SWIFT_RUNTIME_LINK_FLAGS ${shared_cache_link_flags})
+    list(APPEND SWIFT_RUNTIME_SWIFT_LINK_FLAGS ${shared_cache_link_flags})
+endif()
+
 # Build the runtime with -Wall to catch, e.g., uninitialized variables
 # warnings.
 if(SWIFT_COMPILER_IS_MSVC_LIKE)

stdlib/public/Concurrency/CMakeLists.txt

@@ -172,6 +172,7 @@ add_swift_target_library(swift_Concurrency ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
     -diagnostic-style swift
     ${SWIFT_RUNTIME_CONCURRENCY_SWIFT_FLAGS}
   ${swift_concurrency_options}
+  LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}"
   INSTALL_IN_COMPONENT stdlib
   MACCATALYST_BUILD_FLAVOR zippered
 )

stdlib/public/Observation/Sources/Observation/CMakeLists.txt

@@ -29,6 +29,7 @@ add_swift_target_library(swiftObservation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS
 
   C_COMPILE_FLAGS
     ${swift_runtime_library_compile_flags}
+  LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}"
 
   SWIFT_MODULE_DEPENDS _Concurrency
   INSTALL_IN_COMPONENT stdlib