[build] Support installing swift-driver without swiftpm

The install-swift-driver phase knows how to build swift-driver using
CMake. Allowing only install-swift-driver without plain swift-driver
allows installing it without requiring swiftpm.

Author: porglezomp

utils/build-script

@@ -821,7 +821,7 @@ class BuildScriptInvocation(object):
         product_classes = []
         if self.args.build_swiftpm:
             product_classes.append(products.SwiftPM)
-        if self.args.build_swift_driver:
+        if self.args.build_swift_driver or self.args.install_swift_driver:
             product_classes.append(products.SwiftDriver)
         if self.args.build_swiftsyntax:
             product_classes.append(products.SwiftSyntax)