Fix NDK version in Android CI

GCC 4.8.0 - 7.0 has a bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56480) involving specialization in a namespace enclosing the specialized template. This PR fixes an appearance of this bug in the span header.

.github/workflows/android.yml

@@ -29,7 +29,7 @@ jobs:
           echo "Emulator starting"
 
       - name: Configure
-        run: cmake -Werror=dev -DCMAKE_TOOLCHAIN_FILE=$ANDROID_HOME/ndk-bundle/build/cmake/android.toolchain.cmake -DANDROID_PLATFORM=16 -DANDROID_ABI=x86_64 -DCMAKE_BUILD_TYPE=Debug ..
+        run: cmake -Werror=dev -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK_LATEST_HOME/build/cmake/android.toolchain.cmake -DANDROID_PLATFORM=16 -DANDROID_ABI=x86_64 -DCMAKE_BUILD_TYPE=Debug ..
 
       - name: Build
         run: cmake --build . --parallel

include/gsl/span

@@ -343,16 +343,18 @@ namespace details
     };
 }} // namespace gsl::details
 
+namespace std
+{
 template <class Type>
-struct std::pointer_traits<::gsl::details::span_iterator<Type>> {
-    using pointer         = ::gsl::details::span_iterator<Type>;
-    using element_type    = Type;
+struct pointer_traits<::gsl::details::span_iterator<Type>>
+{
+    using pointer = ::gsl::details::span_iterator<Type>;
+    using element_type = Type;
     using difference_type = ptrdiff_t;
 
-    static constexpr element_type* to_address(const pointer i) noexcept {
-        return i.current_;
-    }
+    static constexpr element_type* to_address(const pointer i) noexcept { return i.current_; }
 };
+} // namespace std
 
 namespace gsl { namespace details {
     template <std::size_t Ext>

include/gsl/span_ext

@@ -41,7 +41,7 @@ namespace gsl
 {
 
 // [span.views.constants], constants
-constexpr const std::size_t dynamic_extent = narrow_cast<std::size_t>(-1);
+GSL_INLINE constexpr const std::size_t dynamic_extent = narrow_cast<std::size_t>(-1);
 
 template <class ElementType, std::size_t Extent = dynamic_extent>
 class span;

include/gsl/util

@@ -45,6 +45,12 @@
 #define GSL_NODISCARD
 #endif // defined(__cplusplus) && (__cplusplus >= 201703L)
 
+#if defined(__cpp_inline_variables)
+#define GSL_INLINE inline
+#else
+#define GSL_INLINE
+#endif
+
 namespace gsl
 {
 //