Little-endian PowerPC-64 uses __ieee128 instead of __float128

GCC set a macro re-defining __float128 to __ieee128, but just on this one
architecture. See
https://buildd.debian.org/status/logs.php?pkg=cbmc&arch=ppc64el,
https://buildd.debian.org/status/logs.php?pkg=cbmc&arch=ppc64,
https://buildd.debian.org/status/logs.php?pkg=cbmc&arch=powerpc,
with the build logs for 5.10-2 vs. 5.10-3.

Author: tautschnig

src/ansi-c/ansi_c_internal_additions.cpp

@@ -194,16 +194,21 @@ void ansi_c_internal_additions(std::string &code)
 
     if(
       config.ansi_c.arch == "i386" || config.ansi_c.arch == "x86_64" ||
-      config.ansi_c.arch == "x32" || config.ansi_c.arch == "powerpc" ||
-      config.ansi_c.arch == "ppc64" || config.ansi_c.arch == "ppc64le" ||
-      config.ansi_c.arch == "ia64")
+      config.ansi_c.arch == "x32" || config.ansi_c.arch == "ia64" ||
+      config.ansi_c.arch == "powerpc" || config.ansi_c.arch == "ppc64")
     {
       // https://gcc.gnu.org/onlinedocs/gcc/Floating-Types.html
       // For clang, __float128 is a keyword.
       // For gcc, this is a typedef and not a keyword.
       if(config.ansi_c.mode != configt::ansi_ct::flavourt::CLANG)
         code += "typedef __CPROVER_Float128 __float128;\n";
     }
+    else if(config.ansi_c.arch == "ppc64le")
+    {
+      // https://patchwork.ozlabs.org/patch/792295/
+      if(config.ansi_c.mode != configt::ansi_ct::flavourt::CLANG)
+        code += "typedef __CPROVER_Float128 __ieee128;\n";
+    }
     else if(config.ansi_c.arch == "hppa")
     {
       // https://gcc.gnu.org/onlinedocs/gcc/Floating-Types.html