[clang] [llvm] [AIX] Lower intrinsic __builtin_cpu_is into AIX platform-specific code. (PR #80069)

[Amy Kwan via cfe-commits]

================
@@ -126,4 +126,61 @@ PPC_LNX_CPU("power10",47)
 #undef PPC_LNX_DEFINE_OFFSETS
 #undef PPC_LNX_FEATURE
 #undef PPC_LNX_CPU
+
+// Definition of the following values are found in the AIX header
+// file: </usr/include/sys/systemcfg.h>.
+#ifndef AIX_POWERPC_USE_SYS_CONF
+  #define AIX_POWERPC_USE_SYS_CONF
+  #define AIX_SYSCON_IMPL_IDX 1
+  #define AIX_PPC7_VALUE 0x00008000
+  #define AIX_PPC8_VALUE 0x00010000
+  #define AIX_PPC9_VALUE 0x00020000
+  #define AIX_PPC10_VALUE 0x00040000
+
+  // Supported SUPPORT_METHOD values.
+  #define AIX_BUILTIN_PPC_TRUE 1
+  #define AIX_BUILTIN_PPC_FALSE 0
+  #define USE_SYS_CONF 2
+
+  // Supported COMPARE_OP values.
+  #define COMP_EQ  0
+
+#endif
+
+// The value of SUPPORT_METHOD can be AIX_BUILTIN_PPC_TRUE,
+// AIX_BUILTIN_PPC_FALSE, Or USE_SYS_CONF.
----------------
amy-kwan wrote:

```suggestion
// AIX_BUILTIN_PPC_FALSE, or USE_SYS_CONF.
```

https://github.com/llvm/llvm-project/pull/80069