linking temacs with $(CC) not ld

[Dan Nicolaescu]

Currently ld is used for linking temacs on:
## freebsd, gnu-* not on macppc|ibms390x.
and when CC is not (or does not pretend to be) gcc.

This is situation is very rare, probably has no users, and it's very
likely to have never been tested.   
So we should switch to link $(CC) in that case too.

This will simplify building a bit, we could use $(CFLAGS) on the linker command 
line.
No special hacks would be needed to pass -pg when building with profiling 
enabled, etc.