With tcc4tcl 0.30 (tcc 0.9.26) compiled with MXE GCC 5.4.0, I get the following error:
% tcc4tcl::cproc test {Tcl_WideInt a int b} Tcl_WideInt {return a << b;}
tcc: error: undefined symbol '__ashldi3'
relocating failed
This is only a problem in Windows, and it's working fine in Linux (GCC 8.3.0).
If the << LHS is an int or the RHS is a constant, everything works. Only when the LHS is a Tcl_WideInt (long long) and the RHS is a non-constant _expression_ does __ashldi3 get roped in.
Sorry, I can't upgrade to 0.9.27. tcc4tcl requires 0.9.26.