[SM68] add dxilver check for validation tests. (#6214)

This is to avoid test fail on old validator.

tools/clang/test/HLSLFileCheck/validation/val-SampleCmpBiasGrad-shader-model-ps67.ll

@@ -1,4 +1,4 @@
-; RUN: not %dxv %s 2>&1 | FileCheck %s
+; RUN: %dxilver 1.8 | %dxv %s | FileCheck %s
 
 ;
 ;  Modified base on output of

tools/clang/test/HLSLFileCheck/validation/val-SampleCmpBiasGrad-shader-model-vs67.ll

@@ -1,4 +1,4 @@
-; RUN: not %dxv %s 2>&1 | FileCheck %s
+; RUN: %dxilver 1.8 | %dxv %s | FileCheck %s
 
 ;
 ;  Modified base on output of

tools/clang/test/HLSLFileCheck/validation/val-SampleCmpBiasGrad-shader-model-vs68.ll

@@ -1,4 +1,4 @@
-; RUN: not %dxv %s 2>&1 | FileCheck %s
+; RUN: %dxilver 1.8 | %dxv %s | FileCheck %s
 
 ;
 ;  Modified base on output of

tools/clang/test/HLSLFileCheck/validation/val-SampleCmpBiasGrad.ll

@@ -1,4 +1,4 @@
-; RUN: not %dxv %s 2>&1 | FileCheck %s
+; RUN: %dxilver 1.8 | %dxv %s | FileCheck %s
 
 ;
 ;  Modified base on output of