SPV Version: Emit the requested SPIR-V version, not the header version.

Fixes #1236.

Test/baseResults/hlsl.typeGraphCopy.vert.out

@@ -61,7 +61,7 @@ Shader version: 500
 0:?     'anon@0' (layout( row_major std140) uniform block{ uniform structure{ temp structure{ temp structure{ temp int a,  temp float b} s1,  temp structure{ temp int a,  temp float b} s2} t1,  temp structure{ temp int a,  temp float b} t2,  temp structure{ temp structure{ temp int a,  temp float b} s1,  temp structure{ temp int a,  temp float b} s2} t3} foo})
 0:?     '@entryPointOutput' (layout( location=0) out float)
 
-// Module Version 10200
+// Module Version 10000
 // Generated by (magic number): 80003
 // Id's are bound by 28