Revert "[cxx-interop] Fix check to include std::span"

This reverts commit 2b90ea3.

Author: artemcm

benchmark/utils/CxxTests/CxxStdlibPerformance.h

@@ -5,25 +5,28 @@
 #include <set>
 
 // FIXME swift-ci linux tests do not support std::span
-#ifndef __linux__
+#if defined(__has_include) && __has_include(<span>)
 #include <span>
-#endif // __linux__
+#define SPAN_DEFINED 1
+#else
+#define SPAN_DEFINED 0
+#endif
 
 static const size_t spanSize = 50000;
 
 using VectorOfU32 = std::vector<uint32_t>;
 using SetOfU32 = std::set<uint32_t>;
-#ifndef __linux__
+#if SPAN_DEFINED
 using ArrayOfU32 = uint32_t[spanSize];
 using SpanOfU32 = std::span<uint32_t>;
-#endif // __linux__
+#endif
 
 static inline VectorOfU32 vec;
 static inline SetOfU32 set;
-#ifndef __linux__
+#if SPAN_DEFINED
 static inline ArrayOfU32 array;
 static inline SpanOfU32 span;
-#endif // __linux__
+#endif
 
 inline void initVector(size_t size) {
     if (!vec.empty()) {
@@ -44,7 +47,7 @@ inline void initSet(size_t size) {
     }
 }
 
-#ifndef __linux__
+#if SPAN_DEFINED
 inline void initSpan() {
     if (!span.empty()) {
         return;
@@ -54,7 +57,7 @@ inline void initSpan() {
     }
     span = SpanOfU32(array);
 }
-#endif // __linux__
+#endif
 
 inline VectorOfU32 makeVector32(size_t size) {
     initVector(size);