Merge pull request #80553 from 3405691582/nobtcfi_part2

Use -z,nobtcfi when BTCFI is disabled on OpenBSD.

Author: DougGregor

cmake/modules/AddSwift.cmake

@@ -965,6 +965,11 @@ function(add_swift_host_tool executable)
     endif()
   endif()
 
+  # Opt-out of OpenBSD BTCFI if instructed where it is enforced by default.
+  if(SWIFT_HOST_VARIANT_SDK STREQUAL "OPENBSD" AND SWIFT_HOST_VARIANT_ARCH STREQUAL "aarch64" AND NOT SWIFT_OPENBSD_BTCFI)
+    target_link_options(${executable} PRIVATE "LINKER:-z,nobtcfi")
+  endif()
+
   if(SWIFT_BUILD_SWIFT_SYNTAX)
     set(extra_relative_rpath "")
     if(NOT "${ASHT_BOOTSTRAPPING}" STREQUAL "")