Fix AIX build of PAL because of GCC system header mangling (#30277)
Fix AIX build of PAL because of GCC system header mangling (#30277)

* Fix AIX build of PAL because of GCC system header mangling

GCC's "fix"includes tool claims another function as its victim.
Import the func definition from the headers; we can't trust GCC
to not replace them with "fixed" versions.

(FreeBSD people: `_WITH_GETLINE` to replace what was removed
would help you)

* I figured out why further, explain this BS wrt getline on AIX

* be kinder and to the point

Jiayili1/corefx,ptoonen/corefx,ericstj/corefx,shimingsg/corefx,wtgodbe/corefx,ViktorHofer/corefx,wtgodbe/corefx,shimingsg/corefx,shimingsg/corefx,ericstj/corefx,ericstj/corefx,BrennanConroy/corefx,mmitche/corefx,ptoonen/corefx,ViktorHofer/corefx,mmitche/corefx,wtgodbe/corefx,Jiayili1/corefx,ptoonen/corefx,wtgodbe/corefx,shimingsg/corefx,Jiayili1/corefx,Jiayili1/corefx,Jiayili1/corefx,mmitche/corefx,ViktorHofer/corefx,Jiayili1/corefx,ViktorHofer/corefx,ptoonen/corefx,wtgodbe/corefx,shimingsg/corefx,ptoonen/corefx,ViktorHofer/corefx,Jiayili1/corefx,BrennanConroy/corefx,ericstj/corefx,BrennanConroy/corefx,wtgodbe/corefx,ericstj/corefx,ViktorHofer/corefx,ptoonen/corefx,ptoonen/corefx,mmitche/corefx,mmitche/corefx,wtgodbe/corefx,ericstj/corefx,mmitche/corefx,shimingsg/corefx,ericstj/corefx,shimingsg/corefx,ViktorHofer/corefx,mmitche/corefx