Embed real_value into REAL_CST

Embed real_value into REAL_CST

The following removes the indirection to real_value from REAL_CST
which doesn't seem to serve any useful purpose.  Any sharing can
be achieved by sharing the actual REAL_CST (which is what usually
happens when copying trees) and sharing of real_value amongst
different REAL_CST doesn't happen as far as I can see and would
only lead to further issues like mismatching type and real_value.

2022-04-27  Richard Biener  <rguenther@suse.de>

	* tree-core.h (tree_real_cst::real_cst_ptr): Remove pointer
	to real_value field.
	(tree_real_cst::value): Add real_value field.
	* tree.h (TREE_REAL_CST_PTR): Adjust.
	* tree.cc (build_real): Remove separate allocation.
	* tree-streamer-in.cc (unpack_ts_real_cst_value_fields):
	Likewise.

gcc/cp/
	* module.cc (trees_in::core_vals): Remove separate allocation
	for REAL_CST.