fix cppcorecheck warnings (#703)

* Added c++17 test configurations for clang5.0 and clang6.0

* Fixed CppCoreCheck warnings in GSL and tests

- Added CMakeSettings.json for VS Open Folder configuration
	- So we can easily run CppCoreCheck in VS
- Fixed CppCorecheck warnings where it made sense
- Suppressed the rest
	- Some suppression does not work due to compiler/tool bugs,
          so replaced by #pragma disable
	- CppCoreCheck has noise, suppressed those with comments
	- Catch produces many warnings, blanket-supressed them all
- Had to fix clang formatting to keep attributes in place
	- clang-format does not support attributes, so I am using
        - "CommentPragmas: '^ NO-FORMAT:'" to skip formatiting on them
- Removed GSL_NOEXCEPT macro, removed incorred noexcepts

* Ignore unknown attributes

* ignore unknown attributes in noexception mode tests

* fixed C26472 in at()

* created GSL_SUPPRESS macro to allow all compilers to parse suppression attributes

* try to fix gcc compilation problems with attributes

* ignore gsl::suppress for gcc

* move suppression to function level on return statements

clang5.0 and up does not allow attributes on return statemets in constexpr functions

* move suppression to function level on return statements

* use GSL_SUPPRESS in algorithm_tests

* Addressed PR comments

tests/strided_span_tests.cpp

@@ -14,6 +14,13 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
+#ifdef _MSC_VER
+// blanket turn off warnings from CppCoreCheck from catch
+// so people aren't annoyed by them when running the tool.
+#pragma warning(disable : 26440 26426) // from catch
+
+#endif
+
 #include <catch/catch.hpp> // for AssertionHandler, StringRef, CHECK, CHECK...
 
 #include <gsl/gsl_byte>   // for byte
@@ -71,6 +78,7 @@ TEST_CASE("span_section")
     CHECK((av_section_2[{1, 0}] == 34));
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("strided_span_constructors")
 {
     // Check stride constructor
@@ -271,6 +279,7 @@ TEST_CASE("strided_span_constructors")
     }
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("strided_span_slice")
 {
     std::vector<int> data(5 * 10);
@@ -297,6 +306,7 @@ TEST_CASE("strided_span_slice")
     CHECK(sav[4][9] == 49);
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("strided_span_column_major")
 {
     // strided_span may be used to accommodate more peculiar
@@ -329,6 +339,7 @@ TEST_CASE("strided_span_column_major")
     CHECK((cm_sec[{2, 1}] == 15));
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("strided_span_bounds")
 {
     int arr[] = {0, 1, 2, 3};
@@ -445,6 +456,7 @@ TEST_CASE("strided_span_bounds")
 #endif
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("strided_span_type_conversion")
 {
     int arr[] = {0, 1, 2, 3};
@@ -542,6 +554,8 @@ TEST_CASE("strided_span_type_conversion")
     }
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
 TEST_CASE("empty_strided_spans")
 {
     {
@@ -574,6 +588,8 @@ TEST_CASE("empty_strided_spans")
     }
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
 void iterate_every_other_element(multi_span<int, dynamic_range> av)
 {
     // pick every other element
@@ -599,6 +615,7 @@ void iterate_every_other_element(multi_span<int, dynamic_range> av)
     }
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("strided_span_section_iteration")
 {
     int arr[8] = {4, 0, 5, 1, 6, 2, 7, 3};
@@ -616,6 +633,11 @@ TEST_CASE("strided_span_section_iteration")
     }
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(r.11) // NO-FORMAT: attribute
+GSL_SUPPRESS(r.3) // NO-FORMAT: attribute
+GSL_SUPPRESS(r.5) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
 TEST_CASE("dynamic_strided_span_section_iteration")
 {
     auto arr = new int[8];
@@ -630,6 +652,9 @@ TEST_CASE("dynamic_strided_span_section_iteration")
     delete[] arr;
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute // TODO: does not work
 void iterate_second_slice(multi_span<int, dynamic_range, dynamic_range, dynamic_range> av)
 {
     const int expected[6] = {2, 3, 10, 11, 18, 19};
@@ -656,6 +681,9 @@ void iterate_second_slice(multi_span<int, dynamic_range, dynamic_range, dynamic_
     }
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
 TEST_CASE("strided_span_section_iteration_3d")
 {
     int arr[3][4][2]{};
@@ -670,6 +698,11 @@ TEST_CASE("strided_span_section_iteration_3d")
     }
 }
 
+GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(r.3) // NO-FORMAT: attribute
+GSL_SUPPRESS(r.5) // NO-FORMAT: attribute
+GSL_SUPPRESS(r.11) // NO-FORMAT: attribute
 TEST_CASE("dynamic_strided_span_section_iteration_3d")
 {
     const auto height = 12, width = 2;
@@ -702,6 +735,9 @@ TEST_CASE("dynamic_strided_span_section_iteration_3d")
     delete[] arr;
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
 TEST_CASE("strided_span_conversion")
 {
     // get an multi_span of 'c' values from the list of X's
@@ -720,7 +756,7 @@ TEST_CASE("strided_span_conversion")
     auto d1 = narrow_cast<int>(sizeof(int)) * 12 / d2;
 
     // convert to 4x12 array of bytes
-    auto av = as_multi_span(as_bytes(as_multi_span(arr, 4)), dim(d1), dim(d2));
+    auto av = as_multi_span(as_bytes(as_multi_span(&arr[0], 4)), dim(d1), dim(d2));
 
     CHECK(av.bounds().index_bounds()[0] == 4);
     CHECK(av.bounds().index_bounds()[1] == 12);