[llvm] Enable logf128 constant folding for hosts with 128bit long double (PR #96287)

[Eli Friedman via llvm-commits]

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@@ -11,7 +11,15 @@
 
 namespace llvm {
 
-#if defined(__clang__) && defined(__FLOAT128__) &&                             \
+#if !defined(__LONG_DOUBLE_IBM128__) && (__SIZEOF_LONG_DOUBLE__ == 16) &&      \
+    (__SIZEOF_INT128__ == 16) && (__LDBL_MANT_DIG__ == 113)
+#define HAS_IEE754_FLOAT128
+#if (defined(__GNUC__) && __GNUC__ > 12)
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efriedma-quic wrote:

I'm mostly concerned that checking for __GNUC__ is overly specific, and might break on compilers you haven't seen, or compilers which don't exist yet (e.g. if clang's support for _Float128 changes).

https://github.com/llvm/llvm-project/pull/96287