druntime: redirect dual-ABI functions on glibc to IEEE128 version ... (#20826)

... if IEEE long double ABI is selected

Author: liushuyu

druntime/src/core/stdc/config.d

@@ -670,3 +670,8 @@ package(core) template muslRedirTime64Mangle(string name, string redirectedName)
     else
         enum muslRedirTime64Mangle = name;
 }
+
+version (PPC64)
+    enum PPCUseIEEE128 = real.mant_dig == 113;
+else
+    enum PPCUseIEEE128 = false;