Integrate from maint-5.8:

Integrate from maint-5.8:
[ 18375]
Better version of change #18370; use the new 'E' flag
so that cxinc is exposed (as cpp) only to List::Util
(well, any extension) (well, anyone who does -DPERL_EXT),
no need to export it globally.
p4raw-link: @18375 on //depot/maint-5.8/perl: c8ec9884b4dd9ffdd0a7d1514952a74c55bfab3e
p4raw-link: @18370 on //depot/maint-5.8/perl: 94115b5677e78fbc3321ad88fedfaa3b6bc804bf

p4raw-id: //depot/perl@18551
p4raw-integrated: from //depot/maint-5.8/perl@18545 'copy in'
	ext/List/Util/Makefile.PL (@17645..) 'merge in' embed.fnc
	embed.h global.sym (@18370..)