Another part of github issue 227. Casting a function pointer when
passing it to another function is iffy when lying about the return
type. tputs() expects a routine which returns int, so give it one.
Other xputc() usage is equivalent to putchar(), so define xputc()
with the same function signature as that has.
The tputs() declarations in system.h should probably be changed
(third argument is a function which takes an int rather than
unspecified parameters) but I've left them alone. I made that change
to tputs() in sys/share/tclib.c though.
NT and MSDOS changes are untested. tclib.c compiles ok with clang-
as-gcc on OSX but hasn't been tested with the port that uses it (VMS).
0d76f68f2c