RISC-V: Implement misc macro for vector extensions.

RISC-V: Implement misc macro for vector extensions.

See also:
https://github.com/riscv-non-isa/riscv-c-api-doc/pull/21

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc (riscv_ext_flag_table):
	Update flag name and mask name.
	* config/riscv/riscv-c.cc (riscv_cpu_cpp_builtins): Define
	misc macro for vector extensions.
	* config/riscv/riscv-opts.h (MASK_VECTOR_EEW_32): Rename to ...
	(MASK_VECTOR_ELEN_32): ... this.
	(MASK_VECTOR_EEW_64): Rename to ...
	(MASK_VECTOR_ELEN_64): ... this.
	(MASK_VECTOR_EEW_FP_32): Rename to ...
	(MASK_VECTOR_ELEN_FP_32): ... this.
	(MASK_VECTOR_EEW_FP_64): Rename to ...
	(MASK_VECTOR_ELEN_FP_64): ... this.
	(TARGET_VECTOR_ELEN_32): New.
	(TARGET_VECTOR_ELEN_64): Ditto.
	(TARGET_VECTOR_ELEN_FP_32): Ditto.
	(TARGET_VECTOR_ELEN_FP_64): Ditto.
	(TARGET_MIN_VLEN): Ditto.
	* config/riscv/riscv.opt (riscv_vector_eew_flags): Rename to ...
	(riscv_vector_elen_flags): ... this.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/arch-13.c: New.
	* gcc.target/riscv/arch-14.c: Ditto.
	* gcc.target/riscv/arch-15.c: Ditto.
	* gcc.target/riscv/predef-18.c: Ditto.
	* gcc.target/riscv/predef-19.c: Ditto.
	* gcc.target/riscv/predef-20.c: Ditto.