There are few build and test failures on arm64 platform
with "narrowing conversion" errors. This is due to the char
datatype implementation differences between different platforms
and gcc versions. This commit replaces the char datatype with
the explicit datatype that works across all the platforms.
Updated CI scripts
#786 u8string
#783 Cannot insert existing value to full set
#781 etl::multi_span::iterator::operator *() fails if first span is empty
#780 endian enum_type produces useless-cast warnings
#779 hash.h: warnings produced with -Wfloat-equal
C++14 compiler compatibility
Updated test run scripts
Changed some ETL_ASSERT macros to ETL_ASSERT_OR_RETURN
Changed unit test macros for C++20 compaibility
Updated test run scripts
Updated CMake files to allow C++ standard selection
Replaced ETL_ASSERT_AND_RETURN with ETL_ASSERT_OR_RETURN
Updated C++14 & C++20 unit test compatibility
Changed native char8_t check
Added optional optimisation argument to bash script
