serial_write: change prototype to take a void-pointer buffer.

serial_write: change prototype to take a void-pointer buffer.

While remote.c works with "char *" buffers most of the time, other
remote targets have binary-ish-er protocols, and choose to use
"unsigned char" throughout, like e.g., remote-mips.c or
remote-m32r-sdi.c.  That results in -Wpointer-sign warnings in those
targets, unless we add casts in calls to serial_write.  Since
serial_write is only concerned about sending raw host bytes out, and
serial_ops->write_prim already works with "void *"/"size_t", a similar
interface to the "write" or "send" system calls, I find it natural to
change serial_write's prototype accordingly, avoiding the need for
casts.

Tested on x86_64 Fedora 17, and also by building x86_64-mingw32
and DJGPP/go32 -hosted gdbs.

gdb/
2013-04-19  Pedro Alves  <palves@redhat.com>

	* ser-base.c (ser_base_write): Change prototype -- take 'void *'
	buffer and size_t size.  Adjust.
	* ser-base.h (ser_base_write): Adjust.
	* ser-go32.c (cnts): Change type to size_t.
	(dos_write): Change prototype -- take 'void *'
	buffer and size_t size.  Adjust.
	(dos_info): Print elements of 'cnts' as unsigned long.
	* serial.c (serial_write): Likewise.
	* serial.h (serial_write): Adjust.
	(struct serial_ops) <write>: Change prototype -- take 'void *'
	buffer and size_t size.  Adjust.