Rollup merge of #55564 - smaeul:test-fixes-2, r=alexcrichton

Rollup merge of #55564 - smaeul:test-fixes-2, r=alexcrichton

test/linkage-visibility: Ignore on musl targets

DynamicLibrary uses libc's dlsym() function internally to find symbols.
Some implementations of dlsym(), like musl's, only look at dynamically-
exported symbols, as found in shared libraries. To also export symbols
from the main executable, pass --export-dynamic to the linker.

(Plus see [here](https://stackoverflow.com/questions/4184017) and [here](https://stackoverflow.com/questions/6121838) for examples of where this is necessary on glibc as well.)