Vulkan rules relaxed for glslang C interface

- Added vulkan_rules_relaxed flag to glslang_input_t to turn on Vulkan
  rules relaxed during shader creation.

glslang/Include/glslang_c_interface.h

@@ -166,6 +166,7 @@ typedef struct glslang_input_s {
     glslang_profile_t default_profile;
     int force_default_version_and_profile;
     int forward_compatible;
+    int vulkan_rules_relaxed;
     glslang_messages_t messages;
     const glslang_resource_t* resource;
 } glslang_input_t;