global trees

global trees

This reorders the common and c++ global tree arrays.  It introduces a
module-specific High Water Mark, below which are the immutable slots
initialized at startup and beyond which are the lazily filled slots
(and a few immutables we need to locate by name lookup anyway).

	gcc/c-family/
	* c-common.h (enum c_tree_index): Reorder to place lazy fields
	after newly-added CTI_MODULE_HWM.
	gcc/cp/
	* cp-tree.h (enum cp_tree_index): Reorder to place lazy fields
	after newly-added CPTI_MODULE_HWM.