Add unittest to test collection of C sources and headers

fix typo(s)

Move foreign code from global scope to dub.internal. ...

Avoids conflicting with the actual dub packages when working with dub as a library. Also, even if just by convention, it ensures that dependent code doesn't rely on this code as a public API.

Posix: Add default SONAME/install_name for dynamic libraries ...

Setting it to the filename (ELF) or `@rpath/<file name>` (Mach-O).

This seems to be required in order to use the libraries copied to
the output directory of dependees - either by setting the
LD_LIBRARY_PATH env var when starting the executable, or baking a
RUNPATH into the executable (e.g., via `patchelf --set-rpath` for
deployment).

Otherwise the loader tries to load the library from the original
location specified in the linking cmdline, which is some
`<path to dep pkg>/.dub/…` path (and apparently potentially
relative, and thus even more brittle). For ELF, I would assume
that all SONAME + DT_NEEDED entries (of executable + all .so libs)
would need to be post-processed to enable loading the libs from the
executable's directory (well, any non-original location).

Forward flag `--color={on,off}` to compiler calls (#2382) ...

When the user sets the color mode explicitly,
we forward it to the compiler for consistency,
while making sure it doesn't impact the build cache ID.

Add `fromYAML` method to `Flags` ...

This will be used once Configy starts to parse package recipes.

Trivial: Clear trailing whitespace

Also add options when we combine buildsettings (#2363) ...

* Also add options when we combine buildsettings

* include all the buildsettings in add(bs)

Co-authored-by: WebFreak001 <gh@webfreak.org>

Build{Options,Requirements}: Use a common templated struct ...

A bit less copy-pasta is a small but appreciable win.

Add support for coverage at compile-time (CTFE)

Implement injection of source files from dependencies into parent final binaries (executed/shared libraries)

Fix dependency build settings flooding dflags

Add environment variables to BuildSettings (#2121)

Add lowmem for settings

Filter duplicates in vals input

Revert "Deduplicate dflags and lflags" (#2016) ...

PR #2016 introducted a de-duplication strategy that is too eager and corrupts argument chains, such as "-framework CoreServices -framework CoreFoundation" where the "-framework" argument needs to be duplicated for each framework.

This reverts commit 10bea6f.

Deduplicate dflags and lflags ...

For some reason, dflags and lflags were not using the 'add' convenience function,
which allows to deduplicate flags.
As a result some flags, especially link flags which propagate upwards,
ended up taking half of the command line length.

Replace calls to NativePath.toString() with .name ...

This has been deprecated in vibe-core and only triggers with 'library-nonet'.

extraDependencyFiles attribute added

infer unspecified version filters ...

- otherwise of little use as all dependencies need to have specified
  version filters before this can be used
- also version identifiers are fairly easy to grep for
- cache inferred version filters
- still allows explicit specification for packages that use version
  identifiers in mixins

Added experimental build settings to filter applicable version identifiers ...

Those settings allow to filter version identifiers and debug version identifiers
used during building a package. This can improve the build cache efficiency for
libraries that are used by multiple applications with different version
identifiers.

- only merge filters from source dependencies when the
  dependent has an explicit filter list as well

Pre/post run commands added

Add betterC build option

Fix buildsettings.d according to Sebastian Wilzbach notes ...

Style, NativePath memoizing, more refactoring

See https://github.com/dlang/dub/pull/1335 for details

buildsettings.d refactored to more std library usage

Rename Path to NativePath. ...

Matches the changes done in vibe.d 0.8.x and vibe-core.

Remove compatibility code for DMD frontends < 2.067.x.

add tests for BuildSettings add/remove functions ...

- also convert them to static functions and use a single `private:` attribute

make pic inherited for dynamic libraries

replace slow O(N^2) removeImportFiles with set difference ...

- dub build for a vibe-d project w/o changes (300ms -> 100ms)