Add option to turn UBO layout checks (#260)

* -std430-ubo-layout disables standard UBO layout checks
* TODO: implement all the SSBO layout checks instead
diff --git a/lib/FrontendPlugin.cpp b/lib/FrontendPlugin.cpp
index 400789e..1c6568e 100644
--- a/lib/FrontendPlugin.cpp
+++ b/lib/FrontendPlugin.cpp
@@ -408,6 +408,7 @@
 
             if (is_opencl_kernel &&
                 clspv::Option::ConstantArgsInUniformBuffer() &&
+                !clspv::Option::Std430UniformBufferLayout() &&
                 type->isPointerType() &&
                 type->getPointeeType().getAddressSpace() ==
                     LangAS::opencl_constant) {