[main] expand SVE_VECTOR_OPERATORS to include sizeless vectors (#213)

To guard usage of C/C++ operators on sizeless SVE vectors, we should
expand __ARM_FEATURE_SVE_VECTOR_OPERATORS to include sizeless vectors
and __ARM_FEATURE_SVE_PREDICATE_OPERATORS to include predicate vectors.

It's possible that we also need something in the spec to explain what
these operators do, but right now I would like to get consensus on
what the feature macro should look like so we can add it to clang and
gcc before people start using the operators without it.

Author: David Truby

main/acle.md

@@ -1618,24 +1618,34 @@ SVE language extensions:
 > [The __ARM_FEATURE_SVE_BITS macro](#the-__arm_feature_sve_bits-macro)
 > for details.
 
-**`__ARM_FEATURE_SVE_VECTOR_OPERATORS==1`**
+**`__ARM_FEATURE_SVE_VECTOR_OPERATORS==N`**
 
-> This indicates that applying the `arm_sve_vector_bits` attribute
+> `N >= 1` indicates that applying the `arm_sve_vector_bits` attribute
 > to an SVE vector type creates a type that supports the GNU vector
-> extensions. The state of this macro is only meaningful when
+> extensions. This condition is only meaningful when
 > `__ARM_FEATURE_SVE_BITS` is nonzero. See [`arm_sve_vector_bits` behavior
 > specific to vectors](#arm_sve_vector_bits-behavior-specific-to-vectors)
 > for details.
 
+> `N >= 2` indicates that the operators outlined in the GNU vector
+> extensions additionally work on sizeless SVE vector types like `svint32_t`.
+> The availability of operators on sizeless types is independent of
+> `__ARM_FEATURE_SVE_BITS`.
+
 **`__ARM_FEATURE_SVE_PREDICATE_OPERATORS==1`**
 
-> This indicates that applying the `arm_sve_vector_bits` attribute to
+> `N >= 1` indicates that applying the `arm_sve_vector_bits` attribute to
 > `svbool_t` creates a type that supports basic built-in vector operations.
 > The state of this macro is only meaningful when `__ARM_FEATURE_SVE_BITS`
 > is nonzero. See [`arm_sve_vector_bits` behavior specific to
 > predicates](#arm_sve_vector_bits-behavior-specific-to-predicates)
 > for details.
 
+> `N >= 2` indicates that the built-in vector operations described above
+> additionally work on `svbool_t`.
+> The availability of operators on `svbool_t` is independent of
+> `__ARM_FEATURE_SVE_BITS`.
+
 #### SVE2
 
 `__ARM_FEATURE_SVE2` is defined to 1 if there is hardware support for
@@ -2144,8 +2154,8 @@ be found in [[BA]](#BA).
 | [`__ARM_FEATURE_SVE_MATMUL_FP32`](#multiplication-of-32-bit-floating-point-matrices)                                                                    | 32-bit floating-point matrix multiply extension (FEAT_F32MM)                                       | 1           |
 | [`__ARM_FEATURE_SVE_MATMUL_FP64`](#multiplication-of-64-bit-floating-point-matrices)                                                                    | 64-bit floating-point matrix multiply extension (FEAT_F64MM)                                       | 1           |
 | [`__ARM_FEATURE_SVE_MATMUL_INT8`](#multiplication-of-8-bit-integer-matrices)                                                                            | SVE support for the integer matrix multiply extension (FEAT_I8MM)                                  | 1           |
-| [`__ARM_FEATURE_SVE_PREDICATE_OPERATORS`](#scalable-vector-extension-sve)                                                                               | C and C++ operators support fixed-length SVE predicate types                                       | 1           |
-| [`__ARM_FEATURE_SVE_VECTOR_OPERATORS`](#scalable-vector-extension-sve)                                                                                  | C and C++ operators support fixed-length SVE vector types                                          | 1           |
+| [`__ARM_FEATURE_SVE_PREDICATE_OPERATORS`](#scalable-vector-extension-sve)                                                                               | Level of support for C and C++ operators on SVE vector types                                        | 1           |
+| [`__ARM_FEATURE_SVE_VECTOR_OPERATORS`](#scalable-vector-extension-sve)                                                                                  | Level of support for C and C++ operators on SVE predicate types                                     | 1           |
 | [`__ARM_FEATURE_SVE2`](#sve2)                                                                                                                           | SVE version 2 (FEAT_SVE2)                                                                          | 1           |
 | [`__ARM_FEATURE_SVE2_AES`](#aes-extension)                                                                                                              | SVE2 support for the AES crytographic extension (FEAT_SVE_AES)                                     | 1           |
 | [`__ARM_FEATURE_SVE2_BITPERM`](#bit-permute-extension)                                                                                                  | SVE2 bit permute extension (FEAT_SVE2_BitPerm)                                                     | 1           |