[stdlib] Reinstate AllowUnsafeAttribute experimental feature on libraries

We need this so that older compilers can handle the .swiftinterface
files we generate. It's unnecessary for newer compilers and can be
removed later.

Fixes rdar://148529962.

(cherry picked from commit 0100104)

Author: DougGregor

Runtimes/Core/cmake/modules/ExperimentalFeatures.cmake

@@ -10,4 +10,5 @@ add_compile_options(
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature FreestandingMacros>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature BitwiseCopyable>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature Extern>"
+  "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature AllowUnsafeAttribute>"
   "$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-experimental-feature ValueGenerics>")

stdlib/public/Concurrency/CMakeLists.txt

@@ -66,6 +66,7 @@ list(APPEND SWIFT_RUNTIME_CONCURRENCY_SWIFT_FLAGS
   )
 
 list(APPEND SWIFT_RUNTIME_CONCURRENCY_SWIFT_FLAGS "-strict-memory-safety")
+list(APPEND SWIFT_RUNTIME_CONCURRENCY_SWIFT_FLAGS "-enable-experimental-feature" "AllowUnsafeAttribute")
 
 list(APPEND SWIFT_RUNTIME_CONCURRENCY_C_FLAGS
   "-D__STDC_WANT_LIB_EXT1__=1")

stdlib/public/Cxx/CMakeLists.txt

@@ -23,6 +23,7 @@ add_swift_target_library(swiftCxx STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_ONLY
     -cxx-interoperability-mode=default
     -enable-experimental-feature Span
     -enable-experimental-feature BuiltinModule
+    -enable-experimental-feature AllowUnsafeAttribute
     -strict-memory-safety
     # This module should not pull in the C++ standard library, so we disable it explicitly.
     # For functionality that depends on the C++ stdlib, use C++ stdlib overlay (`swiftstd` module).

stdlib/public/Cxx/std/CMakeLists.txt

@@ -60,6 +60,7 @@ add_swift_target_library(swiftCxxStdlib STATIC NO_LINK_NAME IS_STDLIB IS_SWIFT_O
     # using C++ symbols in resilient overlays (see f4204568).
     -enable-experimental-feature AssumeResilientCxxTypes
 
+    -enable-experimental-feature AllowUnsafeAttribute
     -strict-memory-safety
 
     # The varying modularization of the C++ standard library on different

stdlib/public/Distributed/CMakeLists.txt

@@ -52,6 +52,7 @@ add_swift_target_library(swiftDistributed ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS
   SWIFT_COMPILE_FLAGS
     ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
     -parse-stdlib
+    -enable-experimental-feature AllowUnsafeAttribute
     -strict-memory-safety
 
   LINK_FLAGS

stdlib/public/SwiftOnoneSupport/CMakeLists.txt

@@ -7,7 +7,7 @@ set(swiftOnoneSupport_common_options
 
   "${SWIFT_SOURCE_DIR}/stdlib/linker-support/magic-symbols-for-install-name.c"
 
-  SWIFT_COMPILE_FLAGS "-parse-stdlib" "-Xllvm" "-sil-inline-generics=false" "-Xfrontend" "-validate-tbd-against-ir=none" "-Xfrontend" "-check-onone-completeness" "-Xfrontend" "-disable-access-control" "-strict-memory-safety" "${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}" "${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}"
+  SWIFT_COMPILE_FLAGS "-parse-stdlib" "-Xllvm" "-sil-inline-generics=false" "-Xfrontend" "-validate-tbd-against-ir=none" "-Xfrontend" "-check-onone-completeness" "-Xfrontend" "-disable-access-control" "-strict-memory-safety" "-enable-experimental-feature" "AllowUnsafeAttribute" "${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}" "${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}"
   LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}")
 
 if(CMAKE_BUILD_TYPE STREQUAL "Debug" AND BOOTSTRAPPING_MODE STREQUAL "BOOTSTRAPPING")

stdlib/public/core/CMakeLists.txt

@@ -326,6 +326,7 @@ list(APPEND swift_stdlib_compile_flags "-enable-experimental-feature" "BitwiseCo
 list(APPEND swift_stdlib_compile_flags "-enable-experimental-feature" "ValueGenerics")
 list(APPEND swift_stdlib_compile_flags "-enable-experimental-feature" "AddressableParameters")
 list(APPEND swift_stdlib_compile_flags "-enable-experimental-feature" "AddressableTypes")
+list(APPEND swift_stdlib_compile_flags "-enable-experimental-feature" "AllowUnsafeAttribute")
 list(APPEND swift_stdlib_compile_flags "-strict-memory-safety")
 
 if("${SWIFT_NATIVE_SWIFT_TOOLS_PATH}" STREQUAL "")