[clang] [Clang][TableGen] Support specifying address space in clang builtin prototypes (PR #108497)

[Aaron Ballman via cfe-commits]

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@@ -73,6 +73,13 @@ def Constexpr : Attribute<"E">;
 // Builtin is immediate and must be constant evaluated. Implies Constexpr, and will only be supported in C++20 mode.
 def Consteval : Attribute<"EG">;
 
+// Address space attribute, only valid for pointer or reference arguments.
+// ArgIdx - argument to which the attribute refers. value 0 is for return type.
+// AddrSpaceNum - Address space number for the argument.
+class AddressSpace<int ArgIdx, int AddrSpaceNum> : IndexedAttribute<"", ArgIdx> {
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AaronBallman wrote:

Instead of taking an `int` for the second argument, I think it would make more sense to do:
```
class AddressSpace<int AddrSpaceValue> {
  int SpaceNum = AddrSpaceValue;
}

// Use whatever the correct values are, I just used random numbers
def Global : AddressSpace<12>;
def Constant : AddressSpace<1002>;

class ArgWithAddressSpace<int ArgIdx, AddressSpace Num> : IndexedAttribute<"", ArgIdx< {
  AddressSpace AddrSpace = Num;
}
...
let Attributes = [ArgWithAddressSpace<0, Global>, NoThrow];
```
WDYT?

https://github.com/llvm/llvm-project/pull/108497