Add sonames on musl

[nekopsykose]

the musl platform also supports shared objects having an SONAME, and
this function is called only when making a 'shared object', so this
should always be added

fixes 04a92bc where this was removed
even when generating a dynamic library forcefully by setting library
type to cdylib

fixes #267

[nekopsykose]

reverting all of 04a92bc instead does give warnings with the default -unknown-linux-musl toolchains:

warning: dropping unsupported crate type `cdylib` for target `x86_64-unknown-linux-musl`

(though they are of course harmless)

but when staticlib is used, this code path is entirely unused (it's called shared_object_link_args and only gets called when making a cdylib), so when someone does have a musl toolchain that can make cdylibs, the soname should be there; this conditional was always broken (we are making a shared library but skipping only the soname and nothing else, which doesn't make sense to do)

[nekopsykose]

if there was a way to detect 'target supports cdylib' we could fix #180 too, but i don't think there is a way (without just eating the warnings), so leaving that is fine

[codecov-commenter]

Codecov Report

Merging #268 (4b9bc37) into master (41f5562) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
- Coverage   82.01%   81.99%   -0.02%     
==========================================
  Files          12       12              
  Lines        1846     1844       -2     
==========================================
- Hits         1514     1512       -2     
  Misses        332      332              

Impacted Files	Coverage Δ
src/target.rs	88.88% <100.00%> (-0.16%)	⬇️
src/build.rs	81.56% <0.00%> (-0.02%)	⬇️

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[lu-zero]

Please run rustfmt on your commits :)