Fix xsimd::available_architectures().has() for sve and rvv archs

Ideally the patch CPU detection code should also check if the length
of SVE and RVV is actually supported by the current CPU implementation
(i.e. ZCR_Elx.LEN register for SVE and something else for RVV), but
I don't have such CPUs/emulators handy, so I cannot add such checks.

Given that xsimd::available_architectures().has() is a new feature
of XSIMD13 and the length check has never been present in XSIMD, this
bug is not a regression at least.

The patch also adds a unittest that reproduces the error the patch fixes

include/xsimd/config/xsimd_cpuid.hpp

@@ -42,6 +42,10 @@ namespace xsimd
 #define ARCH_FIELD_EX(arch, field_name) \
     unsigned field_name;                \
     XSIMD_INLINE bool has(::xsimd::arch) const { return this->field_name; }
+
+#define ARCH_FIELD_EX_REUSE(arch, field_name) \
+    XSIMD_INLINE bool has(::xsimd::arch) const { return this->field_name; }
+
 #define ARCH_FIELD(name) ARCH_FIELD_EX(name, name)
 
             ARCH_FIELD(sse2)
@@ -72,8 +76,12 @@ namespace xsimd
             ARCH_FIELD(neon)
             ARCH_FIELD(neon64)
             ARCH_FIELD_EX(i8mm<::xsimd::neon64>, i8mm_neon64)
-            ARCH_FIELD(sve)
-            ARCH_FIELD(rvv)
+            ARCH_FIELD_EX(detail::sve<512>, sve)
+            ARCH_FIELD_EX_REUSE(detail::sve<256>, sve)
+            ARCH_FIELD_EX_REUSE(detail::sve<128>, sve)
+            ARCH_FIELD_EX(detail::rvv<512>, rvv)
+            ARCH_FIELD_EX_REUSE(detail::rvv<256>, rvv)
+            ARCH_FIELD_EX_REUSE(detail::rvv<128>, rvv)
             ARCH_FIELD(wasm)
 
 #undef ARCH_FIELD

test/test_arch.cpp

@@ -38,6 +38,16 @@ struct check_supported
     }
 };
 
+struct check_cpu_has_intruction_set
+{
+    template <class Arch>
+    void operator()(Arch arch) const
+    {
+        static_assert(std::is_same<decltype(xsimd::available_architectures().has(arch)), bool>::value,
+                      "cannot test instruction set availability on CPU");
+    }
+};
+
 struct check_available
 {
     template <class Arch>
@@ -71,6 +81,11 @@ TEST_CASE("[multi arch support]")
         xsimd::supported_architectures::for_each(check_supported {});
     }
 
+    SUBCASE("xsimd::available_architectures::has")
+    {
+        xsimd::all_architectures::for_each(check_cpu_has_intruction_set {});
+    }
+
     SUBCASE("xsimd::default_arch::name")
     {
         constexpr char const* name = xsimd::default_arch::name();