[patch][Driver] -Bprefix option

[Joerg Sonnenberger]

On Fri, Dec 13, 2013 at 01:43:02PM -0500, David Fang wrote:
> 	The attached patch adds help-text to clang -B, and also forwards -B
> to gcc in the Driver, which allows use of newer linker tools.

I don't think the help text is correct -- the path is also used for
other files like crt[01].o IIRC? Forwarding it to GCC is OK.

> 1) Should I do the same for the assembler? (commented out in patch)

No, I don't think it will generally be supported by it.

> 2) How would you advise writing a host-independent test for this
> feature? Create directory with phony 'ld'?  Would -### or -v be
> sufficient to show that gcc/g++ is getting -B?

See test/Driver/prefixed-tools.c -- just add a target that uses the gcc
toolchain.

Joerg