[PR100518] store by mult pieces: keep addr in Pmode

The conversion of a MEM address to ptr_mode in
try_store_by_multiple_pieces was misguided: copy_addr_to_reg expects
Pmode for addresses.


for  gcc/ChangeLog

	PR target/100518
	* builtins.c (try_store_by_multiple_pieces): Drop address
	conversion to ptr_mode.

for  gcc/testsuite/ChangeLog

	PR target/100518
	* gcc.target/aarch64/pr100518.c: New.