Add test to make sure WaveMatrix is not allowed in shader model 6.7 and 6.8 (#6178)

Related to #6133 and #6163.

tools/clang/test/HLSLFileCheck/hlsl/objects/WaveMatrix/WaveMatrix67.hlsl

@@ -0,0 +1,25 @@
+// RUN: %dxc -E main -T cs_6_7 %s | FileCheck %s 
+// RUN: %dxc -E main -T cs_6_8 %s | FileCheck %s
+
+// CHECK-NOT: define void @main()
+
+// CHECK: error: validation errors
+// CHECK: Function: main: error: Opcode WaveMatrix_Annotate not valid in shader model cs_6_{{[7-8]}}
+// CHECK: Function: main: error: Opcode WaveMatrix_Annotate not valid in shader model cs_6_{{[7-8]}}.
+
+RWByteAddressBuffer rwbuf;
+
+[NumThreads(64,1,1)]
+void main(uint3 gtid : SV_GroupThreadID, uint gidx : SV_GroupIndex)
+{
+  WaveMatrixLeft<float, 16, 16> left;
+  WaveMatrixRight<float, 16, 16> right;
+
+// CHECK: WaveMatrix67.hlsl:21:18: error: Opcode WaveMatrix_Depth not valid in shader model cs_6_{{[7-8]}}.
+// CHECK: WaveMatrix67.hlsl:22:18: error: Opcode WaveMatrix_Depth not valid in shader model cs_6_{{[7-8]}}.
+
+  rwbuf.Store(0, left.MatrixDepth());
+  rwbuf.Store(4, right.MatrixDepth());
+}
+
+// CHECK: Validation failed.