packaging lxml failed

Env:
* MacOS 10.14.5
* PyOxidizer 0.2.0
* rustc 1.35.0
* lxml 4.3.4

pyoxidizer.toml rule:
```
[[packaging_rule]]
type = "pip-install-simple"
package = "lxml==4.3.4"
```

some relevant error message:
```
error: linking with `cc` failed: exit code: 1

note: ld: warning: could not create compact unwind for _ffi_call_unix64: does not use RBP or RSP based frame
Undefined symbols for architecture x86_64:
```

Start by reproducing the pip-install-simple packaging_rule for lxml==4.3.4 with the listed PyOxidizer, rustc, and macOS versions. Inspect the complete linker output beyond the excerpt; done means the lxml package builds successfully through this rule without undefined x86_64 symbols.

Written by the indexing model from the issue text.