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

Package.swift

@@ -1,6 +1,16 @@
 // swift-tools-version:5.5
 
 import PackageDescription
+import Foundation
+
+// When building the toolchain on the CI, don't add the CI's runpath for the
+// final build before installing.
+let sourcekitLSPLinkSettings : [LinkerSetting]
+if ProcessInfo.processInfo.environment["SOURCEKIT_LSP_CI_INSTALL"] != nil {
+  sourcekitLSPLinkSettings = [ .unsafeFlags(["-no-toolchain-stdlib-rpath"]) ]
+} else {
+  sourcekitLSPLinkSettings = []
+}
 
 let package = Package(
     name: "SourceKitLSP",
@@ -36,7 +46,8 @@ let package = Package(
           .product(name: "ArgumentParser", package: "swift-argument-parser"),
           .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
         ],
-        exclude: ["CMakeLists.txt"]),
+        exclude: ["CMakeLists.txt"],
+        linkerSettings: sourcekitLSPLinkSettings),
 
       .target(
         name: "SourceKitLSP",
@@ -235,8 +246,6 @@ let package = Package(
 // by the external environment. This allows sourcekit-lsp to take advantage of the automation used
 // for building the swift toolchain, such as `update-checkout`, or cross-repo PR tests.
 
-import Foundation
-
 if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
   // Building standalone.
   package.dependencies += [

Utilities/build-script-helper.py

@@ -188,6 +188,8 @@ def build_single_product(product: str, swift_exec: str, args: argparse.Namespace
     """
     swiftpm_args = get_swiftpm_options(swift_exec, args)
     additional_env = get_swiftpm_environment_variables(swift_exec, args)
+    if args.action == 'install':
+      additional_env['SOURCEKIT_LSP_CI_INSTALL'] = "1"
     cmd = [swift_exec, 'build', '--product', product] + swiftpm_args
     check_call(cmd, additional_env=additional_env, verbose=args.verbose)