SPV: Fix #807: use --hlsl-offsets to allow hlsl-style offsets in a buffer.

Corresponds to the EShMsgHlslOffsets flag in messages.
Works for both GLSL and HLSL.

glslang/Public/ShaderLang.h

@@ -147,6 +147,7 @@ enum EShMessages {
     EShMsgReadHlsl         = (1 << 6),  // use HLSL parsing rules and semantics
     EShMsgCascadingErrors  = (1 << 7),  // get cascading errors; risks error-recovery issues, instead of an early exit
     EShMsgKeepUncalled     = (1 << 8),  // for testing, don't eliminate uncalled functions
+    EShMsgHlslOffsets      = (1 << 9),  // allow block offsets to follow HLSL rules instead of GLSL rules
 };
 
 //