ld does not alias

[Michiel de Bondt]

ld does not replace alias by symbol when import library has .lib 
extension and output is a .dll (-shared). It does if import library has 
.a extension, and also if output is a .exe.

So assume .def file of input dll has line a = b (a is the alias and b is 
the symbol in input dll).
output = exe, import library = .a ===> output searches for symbol b in 
input dll
output = dll, import library = .a ===> output searches for symbol b in 
input dll
output = exe, import library = .lib ===> output searches for symbol b in 
input dll
output = dll, import library = .lib ===> output searches for symbol a in 
input dll