'extern inline' was added in 2fb76c89 for MSVC (it was just
'inline' before), but all of this doesn't really make sense,
the functions are not going to be inlined anyway, and what
'extern inline' means exactly also appears to depend on the
Cxx standard targetted. Let's just remove the 'extern inline'
entirely. At least gcc6 still emits the exact same code as
before anyway. Fixes compilation/linking with gcc 4.8 as
used on L4T on the TK1.