[llvm] RuntimeLibcalls: Add provider libraries for targets to reference (PR #229562)

[Matt Arsenault via llvm-commits]

================
@@ -61,8 +61,11 @@ def IsAAPCS_ABI : LibcallPredicate<[{isAAPCS_ABI(TT, ABIName)}]>;
 def IsEABIVersion
   : LibcallPredicate<[{!TT.isTargetGNUAEABI() && !TT.isTargetMuslAEABI()}]>;
 
-def IsLongDoubleF128 : LibcallPredicate<[{LongDoubleFormat == LongDoubleFormat::IEEEquad}]>;
+// The format of the C `long double` type, which selects the type of the
+// `l`-suffixed libm/compiler-rt entries. Exactly one holds for a module.
----------------
arsenm wrote:

This was never handled correctly, and is out of scope for cleaning up what is already handled 

https://github.com/llvm/llvm-project/pull/229562