When building on OSX, "-L" needs to set the search path for frameworks as well as libraries.

[caryhaynie]

Currently, it appears that

1. rustc disables the standard framework search path by default,
2. the only way to specify an alternative framework search path is via '-C link_args="-F "' to rustc, or by using the oft derided link_args crate attribute.

This makes linking against frameworks via cargo incredibly difficult, since cargo only allows setting the "-l" and "-L" compiler flags. It would be great if rustc modified both the dylib search path and the framework search path when a "-L" option is passed to rustc on OSX.

[alexcrichton]

This seems like #19941 and #19767 play into this quite a bit.

[jonasp]

@alexcrichton suggested in rust-lang/cargo/#1272 to add -L framework=foo which should be translated to -F just like -l framework=foo is being translated into -framework.