[llvm] ARM: Move remaining half convert libcall config into tablegen (PR #153408)

[Matt Arsenault via llvm-commits]

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@@ -1497,6 +1490,27 @@ def ARMHalfConvertLibcallCallingConv : LibcallCallingConv<
     (isAAPCS_ABI(TT, ABIName) ? CallingConv::ARM_AAPCS : CallingConv::ARM_APCS)}]
 >;
 
+def ARMLibgccHalfConvertCalls :
+  LibcallImpls<(add __truncsfhf2, __extendhfsf2),
+    RuntimeLibcallPredicate<[{!TT.isTargetAEABI() && TT.isOSBinFormatMachO()}]>> {
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arsenm wrote:

I tried to do this before, but update_llc_test_checks for some reason breaks on the watchOS triples. I do see no difference with and without this, but those triples also do not use the libcalls in the first place.

Part of the problem I'm trying to solve here is the conflation of does-this-call-exist and will this call be used 

https://github.com/llvm/llvm-project/pull/153408