diff --git a/CMakeLists.txt b/CMakeLists.txt
index fd3facb64df..2474bc12e4e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,24 +42,23 @@ option(SWIFT_SYNTAX_ENABLE_WMO_PRE_3_26
        $<IF:$<AND:$<NOT:$<CONFIG:Debug>>,$<PLATFORM_ID:Darwin>>,YES,NO>)
 
 include(AddSwiftHostLibrary)
-include(SwiftCompilerCapability)
 
-# Don't link with 'string-processing' and 'backtracing'.
-swift_supports_implicit_module("string-processing" SWIFT_SUPPORTS_DISABLE_IMPLICIT_STRING_PROCESSING_MODULE_IMPORT)
-swift_supports_implicit_module("backtracing" SWIFT_SUPPORTS_DISABLE_IMPLICIT_BACKTRACING_MODULE_IMPORT)
-if(SWIFT_SUPPORTS_DISABLE_IMPLICIT_STRING_PROCESSING_MODULE_IMPORT)
-  add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -disable-implicit-string-processing-module-import>")
-endif()
-if(SWIFT_SUPPORTS_DISABLE_IMPLICIT_BACKTRACING_MODULE_IMPORT)
-  add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-Xfrontend -disable-implicit-backtracing-module-import>")
-endif()
-
-# SWIFTSYNTAX_EMIT_MODULE is TRUE by default
-if(NOT DEFINED SWIFTSYNTAX_EMIT_MODULE)
-  set(SWIFTSYNTAX_EMIT_MODULE TRUE)
-endif()
-if(SWIFTSYNTAX_EMIT_MODULE)
-  swift_get_package_cmo_support(SWIFT_PACKAGE_CMO_SUPPORT)
+# Ensure that we do not link the _StringProcessing module. But we can
+# only pass this flag for new-enough compilers that support it.
+file(WRITE "${CMAKE_BINARY_DIR}/tmp/empty-check-string-processing.swift" "")
+execute_process(
+  COMMAND
+    "${CMAKE_Swift_COMPILER}"
+    -Xfrontend -disable-implicit-string-processing-module-import
+    -Xfrontend -parse-stdlib
+    -typecheck "${CMAKE_BINARY_DIR}/tmp/empty-check-string-processing.swift"
+  OUTPUT_QUIET ERROR_QUIET
+  RESULT_VARIABLE
+    SWIFT_SUPPORTS_DISABLE_IMPLICIT_STRING_PROCESSING_MODULE_IMPORT)
+if (NOT SWIFT_SUPPORTS_DISABLE_IMPLICIT_STRING_PROCESSING_MODULE_IMPORT)
+  add_compile_options(
+    $<$<COMPILE_LANGUAGE:Swift>:-Xfrontend>
+    $<$<COMPILE_LANGUAGE:Swift>:-disable-implicit-string-processing-module-import>)
 endif()
 
 # Determine the module triple.
diff --git a/cmake/modules/AddSwiftHostLibrary.cmake b/cmake/modules/AddSwiftHostLibrary.cmake
index a55053de6e6..9c86f847d3c 100644
--- a/cmake/modules/AddSwiftHostLibrary.cmake
+++ b/cmake/modules/AddSwiftHostLibrary.cmake
@@ -87,25 +87,6 @@ function(add_swift_syntax_library name)
       -emit-module-interface-path;${module_interface_file};
       -emit-private-module-interface-path;${module_private_interface_file}
     >)
-
-  # Enable package CMO if possible.
-  if(SWIFT_PACKAGE_CMO_SUPPORT STREQUAL "IMPLEMENTED")
-    target_compile_options("${name}" PRIVATE
-      $<$<COMPILE_LANGUAGE:Swift>:
-        "SHELL:-package-name ${SWIFT_MODULE_ABI_NAME_PREFIX}${PROJECT_NAME}"
-        "SHELL:-Xfrontend -package-cmo"
-        "SHELL:-Xfrontend -allow-non-resilient-access"
-    >)
-  elseif(SWIFT_PACKAGE_CMO_SUPPORT STREQUAL "EXPERIMENTAL")
-    target_compile_options("${name}" PRIVATE
-      $<$<COMPILE_LANGUAGE:Swift>:
-        "SHELL:-package-name ${SWIFT_MODULE_ABI_NAME_PREFIX}${PROJECT_NAME}"
-        "SHELL:-Xfrontend -experimental-package-cmo"
-        "SHELL:-Xfrontend -experimental-allow-non-resilient-access"
-        "SHELL:-Xfrontend -experimental-package-bypass-resilience"
-    >)
-  endif()
-
   if(SWIFT_MODULE_ABI_NAME_PREFIX)
     # ABI name prefix. this can be used to avoid name conflicts.
     target_compile_options("${name}" PRIVATE
diff --git a/cmake/modules/SwiftCompilerCapability.cmake b/cmake/modules/SwiftCompilerCapability.cmake
deleted file mode 100644
index 951e563a49c..00000000000
--- a/cmake/modules/SwiftCompilerCapability.cmake
+++ /dev/null
@@ -1,52 +0,0 @@
-
-# Test if the Swift compiler returns success for supplied compiler arguments....
-function(swift_supports_compiler_arguments out_var)
-  file(WRITE "${CMAKE_BINARY_DIR}/tmp/dummy.swift" "")
-  execute_process(
-    COMMAND "${CMAKE_Swift_COMPILER}" -parse ${ARGN} -
-    INPUT_FILE "${CMAKE_BINARY_DIR}/tmp/dummy.swift"
-    OUTPUT_QUIET ERROR_QUIET
-    RESULT_VARIABLE result
-  )
-  if(NOT result)
-    set("${out_var}" "TRUE" PARENT_SCOPE)
-  else()
-    set("${out_var}" "FALSE" PARENT_SCOPE)
-  endif()
-endfunction()
-
-# Test if the Swift compiler supports -disable-implicit-<module>-module-import.
-macro(swift_supports_implicit_module module_name out_var)
-  swift_supports_compiler_arguments(${out_var}
-    -Xfrontend -disable-implicit-${module_name}-module-import
-  )
-endmacro()
-
-# Get "package cross-module-optimization" compiler arguments suitable for the compiler.
-function(swift_get_package_cmo_support out_var)
-  # > 6.0 : Fixed feature.
-  swift_supports_compiler_arguments(result
-    -package-name my-package
-    -Xfrontend -package-cmo
-    -Xfrontend -allow-non-resilient-access
-  )
-  if(result)
-    set(${out_var} IMPLEMENTED PARENT_SCOPE)
-    return()
-  endif()
-
-  # == 6.0 : Experimental.
-  swift_supports_compiler_arguments(result
-    -package-name my-package
-    -Xfrontend -experimental-package-cmo
-    -Xfrontend -experimental-allow-non-resilient-access
-    -Xfrontend -experimental-package-bypass-resilience
-  )
-  if(result)
-    set(${out_var} EXPERIMENTAL PARENT_SCOPE)
-    return()
-  endif()
-
-  # < 6.0 : Not supported.
-  set(${out_var} NO PARENT_SCOPE)
-endfunction()