[CK] suppress unsafe buffer warn (#687)

incomplete fix from https://github.com/ROCmSoftwarePlatform/composable_kernel/pull/670

So it does not only happen in gtest but also in CK code:

We need to fix them as a quality improvement, but for now suppressing this warning in immediate releases:
http://compiler-ci.amd.com/blue/rest/organizations/jenkins/pipelines/compiler-psdb-amd-stg-open/runs/2540/nodes/282/steps/3202/log/?start=0

e.g.
```
[2023-04-26T17:26:31.524Z] /jenkins/workspace/compiler-psdb-amd-stg-open/Libs/MIOpen/deps_hip/cget/build/tmp-a3db5da587a64213bde99fb856db1b43/composable_kernel-0f98035d/include/ck/utility/generic_memory_space_atomic.hpp:52:19: error: unsafe pointer arithmetic [-Werror,-Wunsafe-buffer-usage]
[2023-04-26T17:26:31.524Z]         atomicAdd(c_style_pointer_cast<float*>(p_dst) + 1, vx.template AsType<float>()[I1]);
[2023-04-26T17:26:31.524Z]                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
```
[2023-04-26T17:26:31.523Z] /jenkins/workspace/compiler-psdb-amd-stg-open/Libs/MIOpen/deps_hip/cget/build/tmp-a3db5da587a64213bde99fb856db1b43/composable_kernel-0f98035d/include/ck/utility/amd_inline_asm.hpp:62:20: error: 'p_a_half2' is an unsafe pointer used for buffer access [-Werror,-Wunsafe-buffer-usage]
[2023-04-26T17:26:31.523Z]     const half2_t* p_a_half2  = c_style_pointer_cast<const half2_t*>(&a);
[2023-04-26T17:26:31.523Z]     ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

cmake/EnableCompilerWarnings.cmake

@@ -92,6 +92,7 @@ else()
                 -Wno-unused-command-line-argument
                 -Wno-weak-vtables
                 -Wno-covered-switch-default
+                -Wno-unsafe-buffer-usage
             )
         else()
             if (CMAKE_${COMPILER}_COMPILER_ID MATCHES "GNU" AND ${COMPILER} MATCHES "CXX")