[gn build] Port a10c9f9

Author: nico

llvm/utils/gn/secondary/compiler-rt/lib/builtins/BUILD.gn

@@ -275,10 +275,9 @@ static_library("builtins") {
     sources -= [ "fp_mode.c" ]
     sources += [
       "cpu_model/x86.c",
-      "i386/fp_mode.c",
       "extendbfsf2.c",
+      "i386/fp_mode.c",
       "truncdfbf2.c",
-      "truncxfbf2.c",
       "truncsfbf2.c",
     ]
     if (long_double_is_80_bits) {