Silence some VC++ compiler warnings

gv.c(1455) : warning C4146: unary minus operator applied to unsigned type, result still unsigned
gv.c(1586) : warning C4146: unary minus operator applied to unsigned type, result still unsigned
gv.c(2122) : warning C4146: unary minus operator applied to unsigned type, result still unsigned
toke.c(12423) : warning C4244: '=' : conversion from 'I32' to 'char', possible loss of data
win32.c(3017) : warning C4022: 'SetHandleInformation' : pointer mismatch for actual parameter 1
win32.c(2971) : warning C4101: 'old_h' : unreferenced local variable
win32.c(2967) : warning C4101: 'oldfd' : unreferenced local variable