Driver: Add new -truncate option

Driver: Add new -truncate option

This commit adds a new option to the driver that truncates one file after
linking.

Tested likeso:

$ gcc hello.c -c
$ du -h hello.o
4.0K  hello.o
$ gcc hello.o -truncate hello.o
$ ./a.out
Hello world
$ du -h hello.o
$ 0   hello.o

$ gcc hello.o -truncate
gcc: error: missing filename after '-truncate'

The motivation for adding this is PR110710. It is used by lto-wrapper to
truncate files in a shell-independent manner.

Signed-off-by: Peter Damianov <peter0x44@disroot.org>
	PR lto/110710
	* common.opt (truncate): New internal option.
	* gcc.cc (totruncate_file): New global.
	(driver_handle_option): Handle -truncate <file>.
	(driver::final_actions): Truncate the file indicated.