Clang cl (#762)

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

* Fix #739 correct cppcorecheck warnings for clang-cl

* Add clang-cl  configurations

* Corrections Appveyor;
Temporarily disable msvc compilation for faster testing (#741)

* Add path to clang-cl.exe (#741)

* Escape backslash in path (#741)

* Update vcpkg (#741)

* Check vcpkg version; try without building vcpkg; use latest clang-cl from path (#741)

* Fix blocks in ps script (#741)

* Try accessing APPVEYOR_BUILD_FOLDER variable (#471)

* Update span size() bug confirmation test for GCC 6.5 (#741)

* MSVC flags to Clang-cl; disable c++98-compat and undefined macro warnings (#741)

* Suppress clang warning on tests (missing-prototypes) (#741)

* Fix clang warning -Wnewline-eof (#741)

* Fix clang warning -Wdouble-promotion (#741)

* Set linker explicitly

* Clean condition statement

* For Clang, fallback to the AppVeyor installed version of CMake

* Fix clang warning -Wmissing-variable-declarations

* Fallback to the MSVC linker until vcpkg has been updated

* Revert "Fallback to the MSVC linker until vcpkg has been updated"

This reverts commit 7263f3289e.

* Fix clang warning -Wunused-member-function

* Fix clang warning -Wmissing-noreturn

* Fix clang warning -Winvalid-noreturn on Windows

* Add macro block end comment on large #if blocks

* Workaround: fallback to mscv link.exe

* Workaround: get msvc paths into PowerShell through intermediate file

* Workaround: fix, remove "PATH=" from text

* Workaround: try with full-path; and return user PATH

* Workaround: fix, escape backslashes

* Revert all since "Workaround: fallback to mscv link.exe" did not work on AppVeyor

This reverts the commits:
bda3d6a428
97062933ac
0f4fb04bac
1b0c19afd1
a5739ea5f0

* Suppress output of git pull; remove vcpkg from cache

* Re-enable AppVeyor builds for all platforms

* Correct typo

Co-Authored-By: Farwaykorse <Farwaykorse@users.noreply.github.com>

* Add Clang-cl 7.0.0 to the supported platforms

* Revert "Fix clang warning -Wunused-member-function"

This reverts commit 6fe1a42035.

* Fix or locally suppress clang warning -Wunused-member-function

* format touched code and correct comment

* git pull --quiet

* fix logic error in workaround

* fix missing bracket

* Suppress output of mkdir

* Replace MSBuild with Ninja

* Suppress output of 7z

* Add architecture flags for Clang

* Drop workaround for lld-link

* 7-zip Overwrite and Alternative output suppression without suppressing errors

Replaces 3c1c0794dd

* AppVeyor setup and CMake before build

* reorder compiler configuration

* remove unnecessary

* remove -fno-strict-aliasing

* remove -Wsign-conversion, since before v4.0 part of -Wconversion

* -Wctor-dtor-privacy is GCC only

* remove -Woverloaded-virtual part of -Wmost, part of -Wall

* add -Wmissing-noreturn

* remove the pragmas for -Wunused-member-function

* Re-add MSBuild generator on AppVeyor

* Print CMake commands

* Add MSBuild toolset selection

* Separate Architecture setting

* clang-cl: add -Weverything

* clang-cl -Wno-c++98-compat

* clang-cl -Wno-c++98-compat-pedantic

* clang-cl -Wno-missing-prototypes

* clang-cl C++14 -Wno-unused-member-function

* clang-cl -Wundef __GNUC__

* clang++: add -Weverything

* clang++ -Wno-c++98-compat

* clang++ -Wno-c++98-compat-pedantic

* clang++ -Wno-missing-prototypes

* clang++ -Wno-weak-vtables

* clang++ C++14 -Wno-unused-member-function

* clang++ fix -Wundef _MSC_VER

* clang++ -Wno-padded

* clang++ solve -Wdeprecated

* Add AppleClang compiler target
Since CMake v3.0 use of Clang for both is deprecated

* clang++ v5.0 C++17 -Wno-undefined-func-template

* Add VS2015 + LLVM/clang-cl to AppVeyor

* Do not disable constexpr when compiling with clang-cl on Windows

* Clean-up clang-only warnings (now under -Weverything)

* Revert "Fix clang warning -Winvalid-noreturn on Windows"

This reverts commit 2238c4760e.

* Suppress -Winvalid-noreturn for the MS STL noexception workaround

* CMake: put preprocessor definition in target_compile_definitions

* Solve compiler warning C4668: __GNUC__ not defined

tests/span_tests.cpp

@@ -37,9 +37,10 @@
 #include <type_traits> // for integral_constant<>::value, is_default_co...
 #include <vector>      // for vector
 
-namespace gsl {
+namespace gsl
+{
 struct fail_fast;
-}  // namespace gsl
+} // namespace gsl
 
 using namespace std;
 using namespace gsl;
@@ -54,9 +55,12 @@ struct DerivedClass : BaseClass
 };
 struct AddressOverloaded
 {
+#if (__cplusplus > 201402L)
+    [[maybe_unused]]
+#endif
     AddressOverloaded operator&() const { return {}; }
 };
-}
+} // namespace
 
 GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("default_constructor")
@@ -513,8 +517,8 @@ TEST_CASE("from_std_array_constructor")
         static span<int> s2;
         s2 = s1;
 
-    #if __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) && __GNUC_PATCHLEVEL__ == 0 &&   \
-    defined(__OPTIMIZE__)
+    #if defined(__GNUC__) && __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) &&      \
+    __GNUC_PATCHLEVEL__ == 0 && defined(__OPTIMIZE__)
         // Known to be broken in gcc 6.4 and 6.5 with optimizations
         // Issue in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83116
         CHECK(s1.size() == 4);