C++ generated string_view breaking for fixed length strings

[kdkavanagh]

On version 1.12.0

g++ -o bin/tests/sbe_unittests_testschema -Wall -Werror -Wextra -std=c++17 -I. -Itests -isystem third tests/sbe/sbecompattest.cpp
./generated/sbe/test_testschema_sbe/TestStrings.h: In member function ‘test::testschema::sbe::TestStrings& test::testschema::sbe::TestStrings::putFixedString(std::string_view)’:
./generated/sbe/test_testschema_sbe/TestStrings.h:330:50: error: ‘using string_view = class std::basic_string_view<char>’ {aka ‘class std::basic_string_view<char>’} has no member named ‘c_str’; did you mean ‘_M_str’?
         std::memcpy(m_buffer + m_offset + 0, str.c_str(), length);
                                                  ^~~~~
                                                  _M_str

[mjpt777]

Fixed with this 6673853