also fixes duplicated emplace_back that *sometimes* breaks single-source
build w/ older toolchains since it would reference the same section twice
> xtensa-lx106-elf/include/c++/4.8.2/bits/vector.tcc:405:31: error: __c causes a section type conflict with __c
> _M_check_len(size_type(1), __EXCSTR("vector::_M_emplace_back_aux"));
(EXCSTR is specific to esp-quick-toolchain, forcing exc text into flash strings instead of using raw literals)