[clang] [HIP][SPIRV] Enable the SPIRV backend instead of the translator through an experimental flag. (PR #162282)

[Shilei Tian via cfe-commits]

================
@@ -0,0 +1,12 @@
+// COM: This test case validates the behavior of -hip-use-experimental-spirv-backend
----------------
shiltian wrote:

No need to use `COM:` prefix for comments.

https://github.com/llvm/llvm-project/pull/162282