[cxx-interop] Add llvm-lit feature 'std_span'

This adds a check in CMake for whether the current C++ stdlib contains the 'span' header. If so, the llvm-lit feature 'std_span' is set. Also adds 'REQUIRES: std_span' to interop tests that include 'span'. This means we no longer have to choose between blanket disabling `std::span` tests on all Linux distributions, or listing every Linux distro with a libstdc++ version without `std::span` support as unsupported. rdar://161999160 rdar://161999174 rdar://162106580 rdar://162106619 rdar://162106643 rdar://162106653 rdar://162106722 rdar://162106747

Author: hnrklssn

test/CMakeLists.txt

@@ -370,6 +370,9 @@ if(NOT "${COVERAGE_DB}" STREQUAL "")
  COMMENT "Touching covering tests")
 endif()
 
+include(CheckIncludeFileCXX)
+check_include_file_cxx("span" HAVE_STD_SPAN)
+
 foreach(SDK ${SWIFT_SDKS})
  foreach(ARCH ${SWIFT_SDK_${SDK}_ARCHITECTURES})
  # macCatalyst needs to run two sets of tests: one with the normal macosx target triple

test/Interop/Cxx/class/access/swiftify-private-fileid.swift

@@ -4,6 +4,7 @@
 // RUN: %target-swift-frontend -emit-ir -I %swift_src_root/lib/ClangImporter/SwiftBridging -plugin-path %swift-plugin-dir %t/blessed.swift -module-name main -I %t/Inputs -o %t/out -Xcc -std=c++20 -cxx-interoperability-mode=default -enable-experimental-feature SafeInteropWrappers -verify
 
 // REQUIRES: swift_feature_SafeInteropWrappers
+// REQUIRES: std_span
 
 //--- Inputs/swiftify-non-public.h
 #pragma once

test/Interop/Cxx/class/safe-interop-mode.swift

@@ -5,6 +5,7 @@
 
 // REQUIRES: objc_interop
 // REQUIRES: swift_feature_LifetimeDependence
+// REQUIRES: std_span
 
 //--- Inputs/module.modulemap
 module Test {

test/Interop/Cxx/stdlib/std-span-interface.swift

@@ -7,6 +7,7 @@
 
 // REQUIRES: swift_feature_SafeInteropWrappers
 // REQUIRES: swift_feature_Lifetimes
+// REQUIRES: std_span
 
 #if !BRIDGING_HEADER
 import StdSpan

test/Interop/Cxx/stdlib/std-span-transformed-execution.swift

@@ -7,6 +7,7 @@
 // REQUIRES: swift_feature_LifetimeDependence
 
 // REQUIRES: executable_test
+// REQUIRES: std_span
 
 #if !BRIDGING_HEADER
 import StdSpan

test/Interop/Cxx/stdlib/use-std-span-typechecker.swift

@@ -1,4 +1,5 @@
 // RUN: %target-typecheck-verify-swift -I %S/Inputs -enable-experimental-cxx-interop -Xcc -std=c++20 2>&1
+// REQUIRES: std_span
 
 import StdSpan
 

test/Interop/Cxx/stdlib/use-std-span.swift

@@ -5,6 +5,7 @@
 // UNSUPPORTED: OS=windows-msvc
 
 // REQUIRES: executable_test
+// REQUIRES: std_span
 
 import StdlibUnittest
 #if !BRIDGING_HEADER

test/Interop/Cxx/swiftify-import/import-as-instance-method.swift

@@ -1,4 +1,5 @@
 // REQUIRES: swift_feature_SafeInteropWrappers
+// REQUIRES: std_span
 
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t

test/Interop/Cxx/swiftify-import/span-in-ctor.swift

@@ -1,4 +1,5 @@
 // REQUIRES: swift_feature_SafeInteropWrappers
+// REQUIRES: std_span
 
 // RUN: rm -rf %t
 // RUN: split-file %s %t

test/Interop/CxxToSwiftToCxx/span/span-execution.cpp

@@ -10,6 +10,7 @@
 // RUN: %target-run %t/swift-cxx-execution | %FileCheck %s
 
 // REQUIRES: executable_test
+// REQUIRES: std_span
 
 //--- header.h
 #include <cstdint>