clang-git support

[marehr]

Keeps track of all changes for clang10

Bugfixes:

• [FIX] initialise std::type_identity in type_list traits ([FIX] initialise std::type_identity in type_list traits seqan3#1557)
• [FIX] clang10: struct / class should be the same in all declarations ([FIX] clang10: struct / class should be the same in all declarations seqan3#1558)
• [FIX] clang: -Wlogical-op-parentheses ([FIX] clang: -Wlogical-op-parentheses seqan3#2055)
• [FIX] clang: use constexpr version of next_power_of_two ([FIX] clang: use constexpr version of std::ceil(std::log2(x)) seqan3#2056)
• [FIX] use feature-testing macro for std::type_identity in type_traits ([FIX] use feature-testing macro for std::type_identity in type_traits seqan3#2057)
• [TEST] simplify overly complicated decltype in single_pass_input_test ([TEST] simplify overly complicated decltype in single_pass_input_test seqan3#2058)

Reported Compiler Bugs:

• header is missing __cpp_lib_type_identity and other macros (https://bugs.llvm.org/show_bug.cgi?id=47261)
• deleted functions in requires clauses don't SFINAE in concepts (https://bugs.llvm.org/show_bug.cgi?id=44833)
• [trunk] Assertion `!isValueDependent() && "Expression evaluator can't be called on a dependent expression."' failed. ([trunk] Assertion `!isValueDependent() && "Expression evaluator can't be called on a dependent expression."' failed. saarraz/clang-concepts-monorepo#54)
• Concept causes infinite loops at compile time (-Wstack-exhausted) (https://bugs.llvm.org/show_bug.cgi?id=44959)
• ICE with concepts (https://bugs.llvm.org/show_bug.cgi?id=47174)
• [concepts] [ice] substitution into constraint expression resulted in a non-constant expression (https://bugs.llvm.org/show_bug.cgi?id=51503)
• [concepts] [ice] deduction guide (https://bugs.llvm.org/show_bug.cgi?id=51537)

Follow up tasks:

• update supported platforms: http://docs.seqan.de/seqan/3-master-user/setup.html and https://github.com/seqan/seqan3/blob/master/README.md

[eseiler]

Closing, will reopen a new Compiler support meta issue.