Use newer split module flag with Swift 5.4

Uses the newer `-experimental-skip-non-inlinable-function-bodies-without-types` which was introduced here: swiftlang/swift#34612. This should improve LLDB usage in some cases.

When using WMO, it has two downsides in Swift 5.5, both introduced by swiftlang/swift#38939:
- The swiftmodules will have swiftdeps info embedded in them, which is only needed for incremental compilation
- Interface hashing is enabled, which again is only needed for incremental compilation

This is because the swift compiler only expects `-experimental-skip-non-inlinable-function-bodies-without-types` to be used with the new `emit-module-separately` incremental build.

Author: brentleyjones

swift/internal/feature_names.bzl

@@ -316,9 +316,14 @@ SWIFT_FEATURE_GENERATE_PATH_TO_UNDERSCORES_FROM_PROTO_FILES = "swift.generate_pa
 SWIFT_FEATURE_SPLIT_DERIVED_FILES_GENERATION = "swift.split_derived_files_generation"
 
 # If enabled the skip function bodies frontend flag is passed when using derived
-# files generation. This requires Swift 5.2
+# files generation. This requires Swift 5.2.
 SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES = "swift.skip_function_bodies_for_derived_files"
 
+# If enabled the skip function bodies without types frontend flag is passed when
+# using derived files generation. This takes precedence over
+# swift.skip_function_bodies_for_derived_files. This requires Swift 5.4.
+SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES = "swift.skip_function_bodies_without_types_for_derived_files"
+
 # If enabled remap the absolute path to Xcode in debug info. When used with
 # swift.coverage_prefix_map also remap the path in coverage data.
 SWIFT_FEATURE_REMAP_XCODE_PATH = "swift.remap_xcode_path"

swift/internal/features.bzl

@@ -29,6 +29,7 @@ load(
     "SWIFT_FEATURE_ENABLE_BARE_SLASH_REGEX",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES",
     "SWIFT_FEATURE_ENABLE_TESTING",
     "SWIFT_FEATURE_ENABLE_V6",
     "SWIFT_FEATURE_FILE_PREFIX_MAP",
@@ -257,6 +258,7 @@ def default_features_for_toolchain(target_triple):
         SWIFT_FEATURE_ENABLE_BARE_SLASH_REGEX,
         SWIFT_FEATURE_ENABLE_BATCH_MODE,
         SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES,
+        SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES,
         SWIFT_FEATURE_FILE_PREFIX_MAP,
         SWIFT_FEATURE_INTERNALIZE_AT_LINK,
         SWIFT_FEATURE_OPT_USES_WMO,

swift/toolchains/config/compile_config.bzl

@@ -55,6 +55,7 @@ load(
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_LIBRARY_EVOLUTION",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
+    "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES",
     "SWIFT_FEATURE_ENABLE_TESTING",
     "SWIFT_FEATURE_ENABLE_V6",
     "SWIFT_FEATURE_FASTBUILD",
@@ -1119,6 +1120,14 @@ def compile_action_configs(
                 add_arg("-experimental-skip-non-inlinable-function-bodies"),
             ],
             features = [SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES],
+            not_features = [SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES],
+        ),
+        ActionConfigInfo(
+            actions = [SWIFT_ACTION_DERIVE_FILES],
+            configurators = [
+                add_arg("-experimental-skip-non-inlinable-function-bodies-without-types"),
+            ],
+            features = [SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES_WITHOUT_TYPES],
         ),
 
         # Configure index-while-building.

test/split_derived_files_tests.bzl

@@ -409,6 +409,7 @@ def split_derived_files_test_suite(name, tags = []):
         mnemonic = "SwiftCompile",
         not_expected_argv = [
             "-experimental-skip-non-inlinable-function-bodies",
+            "-experimental-skip-non-inlinable-function-bodies-without-types",
         ],
         tags = all_tags,
         target_under_test = "//test/fixtures/debug_settings:simple",
@@ -417,11 +418,12 @@ def split_derived_files_test_suite(name, tags = []):
     split_swiftmodule_skip_function_bodies_test(
         name = "{}_skip_function_bodies".format(name),
         expected_argv = [
-            "-experimental-skip-non-inlinable-function-bodies",
+            "-experimental-skip-non-inlinable-function-bodies-without-types",
         ],
         mnemonic = "SwiftDeriveFiles",
         not_expected_argv = [
             "-emit-object",
+            "-experimental-skip-non-inlinable-function-bodies",
         ],
         tags = all_tags,
         target_under_test = "//test/fixtures/debug_settings:simple",