parsing cargo:rustc-flags does not support the -L/libdir syntax (no spaces between flag and argument)

[filmil]

Problem

Steps

1. See: https://github.com/rust-lang/cargo/blob/master/src/cargo/core/compiler/custom_build.rs#L514
2. Note that the parsing algorithm requires a space between the flag and the flag value.
3. However, utilities like pkg-config will often print something like: -L/some/dir/local/lib -licui18n -licuuc -licudata, which is correct as far as flags go, but won't parse.

Possible Solution(s)

Perhaps the parsing should be corrected to account for this. And yes, I can replace -L with -L (space at end) and do the same for -l but would be nice if this worked out of the box.

Notes

Output of cargo version:

╰─>$ cargo version
cargo 1.37.0-nightly (4c1fa54d1 2019-06-24)

[RobMor]

Hi, I've gone ahead and taken a look at this. I believe I fixed the issue in my own fork and would like to write some tests for it. I'm brand new to cargo (and open source contributions in general) and don't really know where these tests would go. Right now I'm thinking tests/testsuite/build_script.rs would be a good place?

Also, judging by the other tests in that file, simply calling the parse_rustc_flags function in the usual unit-testing fashion is not what I should do?