Drop C++ standard tests for compilers which do not implement required…

… features.

Signed-off-by: Richard Musil <[email protected]>

tests/CMakeLists.txt

@@ -21,6 +21,11 @@ include(test)
 # override standard support
 #############################################################################
 
+# Clang only supports C++14 starting from Clang 3.5 (lesser versions miss std::enable_if_t)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.5)
+    unset(compiler_supports_cpp_14)
+endif()
+
 # Clang only supports C++17 starting from Clang 5.0
 if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
     unset(compiler_supports_cpp_17)
@@ -29,6 +34,10 @@ endif()
 if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.1)
     unset(compiler_supports_cpp_17)
 endif()
+# GCC 5 and 6 do claim experimental support for C++17, but do not implement <optional>
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.0)
+    unset(compiler_supports_cpp_17)
+endif()
 
 # Clang C++20 support appears insufficient prior to Clang 9.0 (based on CI build failure)
 if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)