Re-configuring assembler in Gradle

I am trying to use the assembler plugin to assemble and link .s files in my project. I will be launching my assembler from the gcc compiler as follows:

sparc-rtems-gcc -x assembler-with-cpp -c start.s -o start.o

However, I am unable to do it. By default, Gradle always adds the -x assembler flag and my build fails. Here is the excerpt from build.gradle

// build.gradle for startup

apply plugin: 'assembler'

model {

	toolChains {
		gcc(Gcc) {
			path "/opt/rtems/4.6_20130612/bin"
			eachPlatform {
				assembler.executable = "sparc-rtems-gcc"
				linker.executable = "sparc-rtems-ld"				
			assembler.withArguments { args ->
				args << "-x assembler-with-cpp"
			linker.withArguments {

What is wrong in my set-up? I am using Gradle version 3.0