[Bug target/78230] Compile pr66178.c fail for mips64el-elf with N64 abi

[npickito at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78230

--- Comment #2 from Kito Cheng <npickito at gmail dot com> ---
Ya, In fact I am working on RISV-V 64, and it's seem cause by
TRULY_NOOP_TRUNCATION (32, 64) == false.