aarch64: Simplify generation of .arch strings

aarch64: Simplify generation of .arch strings

aarch64-common.cc has two arrays, one maintaining the original
definition order and one sorted by population count.  Sorting
by population count was a way of ensuring topological ordering,
taking advantage of the fact that the entries are partially
ordered by the subset relation.  However, the sorting is not
needed now that the .def file is forced to have topological
order from the outset.

Other changes are:

(1) The population count used:

      uint64_t total_flags_a = opt_a->flag_canonical & opt_a->flags_on;
      uint64_t total_flags_b = opt_b->flag_canonical & opt_b->flags_on;
      int popcnt_a = popcount_hwi ((HOST_WIDE_INT)total_flags_a);
      int popcnt_b = popcount_hwi ((HOST_WIDE_INT)total_flags_b);

    where I think the & was supposed to be |.  This meant that the
    counts would always be 1 in practice, since flag_canonical is
    a single bit.  This led us to printing +nofp+nosimd even though
    GCC "knows" (and GAS agrees) that +nofp disables simd.

(2) The .arch output code converts +aes+sha2 to +crypto.  I think
    the main reason for doing this is to support assemblers that
    predate the individual per-feature crypto flags.  It therefore
    seems more natural to treat it as a special case, rather than
    as an instance of a general pattern.  Hopefully we won't do
    something similar in future!

    (There is already special handling of CRC, for different reasons.)

(3) Previously, if the /proc/cpuinfo code saw a feature like sve,
    it would assume the presence of all the features that sve
    depends on.  It would be possible to keep that behaviour
    if necessary, but it was simpler to assume the presence of
    fp16 (say) only when fphp is present.  There's an argument
    that that's more conservatively correct too.

gcc/
	* common/config/aarch64/aarch64-common.cc
	(TARGET_OPTION_INIT_STRUCT): Delete.
	(aarch64_option_extension): Remove is_synthetic_flag.
	(all_extensions): Update accordingly.
	(all_extensions_by_on, opt_ext, opt_ext_cmp): Delete.
	(aarch64_option_init_struct, aarch64_contains_opt): Delete.
	(aarch64_get_extension_string_for_isa_flags): Rewrite to use
	all_extensions instead of all_extensions_on.

gcc/testsuite/
	* gcc.target/aarch64/cpunative/info_8: Add all dependencies of sve.
	* gcc.target/aarch64/cpunative/info_9: Likewise svesm4.
	* gcc.target/aarch64/cpunative/info_15: Likewise.
	* gcc.target/aarch64/cpunative/info_16: Likewise sve2.
	* gcc.target/aarch64/cpunative/info_17: Likewise.
	* gcc.target/aarch64/cpunative/native_cpu_2.c: Expect just +nofp
	rather than +nofp+nosimd.
	* gcc.target/aarch64/cpunative/native_cpu_10.c: Likewise.
	* gcc.target/aarch64/target_attr_15.c: Likewise.