gcc/ChangeLog:

	* common/config/riscv/riscv-common.c
	(riscv_subset_list::parse_multiletter_ext): Checking multiletter
	extension has more than 1 letter.

gcc/testsuite/ChangeLog

	* gcc.target/riscv/arch-7.c: New.
	* gcc.target/riscv/attribute-10.c: Update test arch string.