Add back -no-toolchain-stdlib-rpath when installing sourcekit-lsp

Pull #597 incorrectly removed this, as it's still needed on ELF platforms.

Author: finagolfin

Utilities/build-script-helper.py

@@ -224,6 +224,7 @@ def install(swift_exec: str, args: argparse.Namespace) -> None:
     swiftpm_args = get_swiftpm_options(swift_exec, args)
     additional_env = get_swiftpm_environment_variables(swift_exec, args)
     bin_path = swiftpm_bin_path(swift_exec, swiftpm_args=swiftpm_args, additional_env=additional_env)
+    swiftpm_args += ['-Xswiftc', '-no-toolchain-stdlib-rpath']
 
     for prefix in args.install_prefixes:
         install_binary('sourcekit-lsp', bin_path, os.path.join(prefix, 'bin'), verbose=args.verbose)