libgomp.texi: Note to 'Memory allocation' sect and missing mem-memory routines

libgomp.texi: Note to 'Memory allocation' sect and missing mem-memory routines

This commit completes the documentation of the OpenMP memory-management
routines, except for the unimplemented TR11 additions.  It also makes clear
in the 'Memory allocation' section of the 'OpenMP-Implementation Specifics'
chapter under which condition OpenMP managed memory/allocators are used.

libgomp/ChangeLog:

	* libgomp.texi: Fix some typos.
	(Memory Management Routines): Document remaining 5.x routines.
	(Memory allocation): Make clear when the section applies.