build-script: add a flag to separately install SwiftSyntax artifacts.

This flag '--swiftsyntax-install-prefix' could be used in the preset mode
to specify an installation dir. If we are building SwiftSyntax without building
the rest of the compiler, we'll install the SwiftSyntax modules and dylibs
with lib_InternalSwiftSyntaxParser.dylib to the given directory directly, ignoring
the conventional toolchain locations.

Author: nkcsgexi

utils/build-script

@@ -993,8 +993,10 @@ def main_preset():
         help="Print the expanded build-script invocation generated "
              "by the preset, but do not run the preset",
         action=arguments.action.optional_bool)
+    parser.add_argument(
+        "--swiftsyntax-install-prefix",
+        help="specify the directory to where SwiftSyntax should be installed")
     args = parser.parse_args()
-
     if len(args.preset_file_names) == 0:
         args.preset_file_names = [
             os.path.join(
@@ -1044,6 +1046,10 @@ def main_preset():
         build_script_args += ["--distcc"]
     if args.build_jobs:
         build_script_args += ["--jobs", str(args.build_jobs)]
+    if args.swiftsyntax_install_prefix:
+        build_script_args += ["--install-swiftsyntax",
+                              "--install-destdir",
+                              args.swiftsyntax_install_prefix]
 
     diagnostics.note('using preset "{}", which expands to \n\n{}\n'.format(
         args.preset, shell.quote_command(build_script_args)))

utils/build-script-impl

@@ -3566,8 +3566,18 @@ for host in "${ALL_HOSTS[@]}"; do
                     exit 1
                 fi
                 echo "--- Installing ${product} ---"
-                DYLIB_DIR="${host_install_destdir}${host_install_prefix}/lib/swift/${SWIFT_HOST_VARIANT}"
-                MODULE_DIR="${DYLIB_DIR}/${SWIFT_HOST_VARIANT_ARCH}"
+                if [ "${BUILD_LIBPARSER_ONLY}" ]; then
+                    # We don't have a toolchain so we should install to the specified dir
+                    DYLIB_DIR="${INSTALL_DESTDIR}"
+                    MODULE_DIR="${INSTALL_DESTDIR}"
+                    # Install libParser is necessary
+                    rsync -a "$(build_directory ${host} swift)/lib/lib_InternalSwiftSyntaxParser.dylib" "${INSTALL_DESTDIR}"
+                else
+                    # We have a toolchain so install to the toolchain
+                    DYLIB_DIR="${host_install_destdir}${host_install_prefix}/lib/swift/${SWIFT_HOST_VARIANT}"
+                    MODULE_DIR="${DYLIB_DIR}/${SWIFT_HOST_VARIANT_ARCH}"
+                fi
+
                 if [[ -z "${SKIP_INSTALL_SWIFTSYNTAX_MODULE}" ]] ; then
                     call "${swiftsyntax_build_command[@]}" --dylib-dir="${DYLIB_DIR}" --swiftmodule-dir "${MODULE_DIR}" --install
                 else