[libclc] [libclc] Support the generic address space (PR #137183)

[Matt Arsenault via cfe-commits]

================
@@ -23,4 +23,20 @@
 #define _CLC_DEF __attribute__((always_inline))
 #endif
 
+#if __OPENCL_C_VERSION__ == CL_VERSION_2_0 ||                                  \
+    (__OPENCL_C_VERSION__ >= CL_VERSION_3_0 &&                                 \
+     defined(__opencl_c_generic_address_space))
+#define _CLC_GENERIC_AS_SUPPORTED 1
+// Note that we hard-code the assumption that a non-distinct address space means
+// that the target maps the generic address space to the private address space.
+#ifdef __CLC_DISTINCT_GENERIC_ADDRSPACE__
+#define _CLC_DISTINCT_GENERIC_AS_SUPPORTED 1
+#else
+#define _CLC_DISTINCT_GENERIC_AS_SUPPORTED 0
+#endif
+#else
----------------
arsenm wrote:

Even if not this, the current name is misleading. It's not about generic being supported, if anything it's more like private isn't real 

https://github.com/llvm/llvm-project/pull/137183