[clang] [llvm] [AIX] support builtin_cpu_is() for aix (PR #80069)

[Amy Kwan via llvm-commits]

================
@@ -126,4 +126,57 @@ PPC_LNX_CPU("power10",47)
 #undef PPC_LNX_DEFINE_OFFSETS
 #undef PPC_LNX_FEATURE
 #undef PPC_LNX_CPU
+
+// Definition of following value are found in the AIX header file <systemcfg.h>
+#ifndef AIX_POWERPC_SYS_CONF
+#define AIX_POWERPC_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
+
+#define AIX_BUILTIN_PPC_TRUE 1
+#define AIX_BUILTIN_PPC_FALSE 0
+#define COMP_OP 2
+
+#define OP_EQ  0
+
+#endif
+
+//The value of SUPPORT is COMP_OP, it means the feature depend on the V(INDEX)&MASK OP VALUE
+//If the value of MASK is zero, it means we do not need to do mask, just check V(INDEX) OP VALUE.
+
+#ifndef PPC_AIX_CPU
+#define PPC_AIX_CPU(NAME, SUPPORT, INDEX, MASK, OP, VALUE)
+#endif
+
+//Since the __builtin_cpu_is() is supported only on AIX7.2 or AIX7.2 later OS.
+//And AIX 7.2 is supported only on IBM POWER 7 and later processors.
+//The __builtin_cpu_is() function returns false for other CPUs which are not Power7 and Power7 up.
----------------
amy-kwan wrote:

```suggestion
// __builtin_cpu_is() is supported only on AIX 7.2 or AIX 7.2 later,
// and AIX 7.2 is supported only on IBM POWER 7 and later processors.
// This means that __builtin_cpu_is() returns false for other CPUs which are not Power7 and up.
```
This might be a bit more clearer.

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