search linker scripts in cwd first

[spookyvision]

harmonize linker script directory search order with non-flip-link linkers to reduce surprises.
Specifically, other crates might introduce spurious and potentially wrong memory.x scripts, this PR attempts to do some damage control by searching the current working directory first

[japaric]

looks good to me! but clippy is unhappy on some existing code. could you please do a drive-by fix? (I think I've seen that warning before and it was a false positive iirc; if that's the case silencing it with #[allow] is fine)

[japaric]

bors r+

[bors]

Build succeeded:

• ci