Build Script Overrides involving library names with periods in them fail

[qdot]

In a project that is trying to use the libusb-sys (https://github.com/dcuddeback/libusb-sys) crate on windows, I was trying to override the usb library requirement since windows doesn't have pkg_config. In libusb-sys, the library is specified as:

links="usb-1.0"

I added the following block to my ~/.cargo/config, escaping as recommended by TOML for table names with periods in them:

[target.x86_64-pc-windows-gnu.'usb-1.0']
rustc-link-search = ["c:\\Users\\qdot\\code\\libusb-1.0"]
rustc-link-lib = ["usb-1.0"]

On trying to build, I got the following error and backtrace

C:\Users\qdot\code\libusb-sys>cargo build --verbose
thread '<main>' panicked at 'called `Option::unwrap()` on a `None` value', ../src/libcore\option.rs:325
stack backtrace:
   0:           0x9410aa - std::panicking::default_hook::_$u7b$$u7b$closure$u7d$$u7d$::hca543c34f11229ac
   1:           0x9405e7 - std::panicking::default_hook::hc2c969e7453d080c
   2:           0x90539b - std::panicking::rust_panic_with_hook::hfe203e3083c2b544
   3:           0x9423f5 - std::panicking::begin_panic::h4889569716505182
   4:           0x906ed5 - std::panicking::begin_panic_fmt::h484cd47786497f03
   5:           0x94205c - rust_begin_unwind
   6:           0x956185 - core::panicking::panic_fmt::h257ceb0aa351d801
   7:           0x956c90 - core::panicking::panic::h4bb1497076d04ab9
   8:           0x50f6f1 - cargo::ops::cargo_compile::scrape_target_config::h3ac6edc0324e7a3b
   9:           0x4f82f4 - cargo::ops::cargo_compile::compile_pkg::h48656ffa9b1541f3
  10:           0x4f58c6 - cargo::ops::cargo_compile::compile::h1b43b20047c53d10
  11:           0x419070 - cargo::call_main_without_stdin::hec0ecdd41bac3cd3
  12:           0x40845a - cargo::execute::hab7accd6bf9b5c64
  13:           0x404a79 - cargo::call_main_without_stdin::hf099bd36acb849a3
  14:           0x401a4c - cargo::main::h2b219a79f378c1ef
  15:           0x93fcdc - std::panicking::try::call::hc5e1f5b484ec7f0e
  16:           0x950838 - _rust_maybe_catch_panic
  17:           0x93fad4 - std::rt::lang_start::h61f4934e780b4dfc
  18:           0x4013b4 - _tmainCRTStartup
  19:           0x4014e7 - mainCRTStartup
  20:     0x7fffb14c0403 - mz_zip_writer_add_to_central_dir.constprop.18 

It looks like this may be due to how cargo breaks apart TOML table names then reassembles them to find build override commands, around https://github.com/rust-lang/cargo/blob/5a26b65/src/cargo/ops/cargo_compile.rs#L491-L492