[SwiftSyntax] Add CMake argument to enable assertions in SwiftSyntax for Release+Assert builds

This does not do anything by itself, it needs a corresponding change in swift-syntax to pick up the CMake option and actually enable assertions.

Author: ahoppen

utils/swift_build_support/swift_build_support/products/earlyswiftsyntax.py

@@ -54,6 +54,7 @@ def build(self, host_target):
         self.generate_toolchain_file_for_darwin_or_linux(host_target)
 
         self.cmake_options.define('CMAKE_INSTALL_PREFIX:PATH', self.args.install_prefix)
+        self.cmake_options.define('SWIFTSYNTAX_ENABLE_ASSERTIONS:BOOL', self.args.assertions)
         self.build_with_cmake(["all"], self.args.swift_build_variant, [])
 
     def should_test(self, host_target):