arch/mips64el: remove -fprefetch-loop-arrays

[jyhi]

• This is not a platform-specific flag, and should not be placed here.
• '-fprefetch-loop-arrays' is a hard optimization -- it might be opened on some softwares operating huge arrays, like databases, but not the whole system.

[MingcongBai]

'-fprefetch-loop-arrays' is a hard optimization -- it might be opened on some softwares operating huge arrays, like databases, but not the whole system.

Consider merging to _common.sh?

[jyhi]

Consider merging to _common.sh?

No, this optimization does little good to other software -- what's worse, it may generate big binaries. Not recommended if opening it on the whole system. Might consider using it on MySQL or else.

[MingcongBai]

Okay. Taking your word for it.