Add unittest to test collection of C sources and headers

reduce dependency on the working directory ...

Improves library API usage and bugs with the build generator

Reduce dependency on `std.file` (#2547)

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.

LDC: Use `-fvisibility=public -dllimport=all` when compiling a Windows DLL (#2412) ...

As `-shared` can only be used when linking the DLL in the same cmdline too.
On Windows, `-shared` changes the defaults of some important settings wrt.
dllim/export, so specify those explicitly when *compiling* a DLL with dub
(or some static lib dependency thereof etc.).

Keep logging functionality out of the public API as requested in https://github.com/dlang/dub/pull/2124#issuecomment-813016939.

New logging module - initial functionality ...

The new module replaces dub.internal.vibecompat.core.log by using the
same function names, but implementing colored output and the left
fixed-width tag. Overloaded functions are provided to output colored
text.

Still missing initLogging() and non-TTY stdout/stderr detection

compilers: Change lflagsToDFlags to avoid scope escape ...

If 'in' implies 'scope', then the parameter is being escaped.

Add support for coverage at compile-time (CTFE)

add UnsupportedArchitecture/CompilerException ...

for API purposes to not match on string prefixes

Merge remote-tracking branch 'upstream/stable' into merge_stable

LDC: Recognize `-gcc` as linker D flag ...

As it affects the invoked C compiler for linking.

Add environment variables to BuildSettings (#2121)

Add lowmem for settings

Remove unused imports.

Remove unused selective imports. These are private imports of symbols that do not occur elsewhere in the file, so they are safe to be removed.

Make {DMD,LDC}Compiler.isLinkerDFlag() public ...

E.g., this is useful for Reggae too.

Merge remote-tracking branch 'upstream/master' into stable

Improved ldc cross compile: ...

The folder `.dub/obj` has been moved to `.dub/build-*/obj` for an independent cross / parallel build process.
Now it is possible that two processes can build the same project with different configurations.

Add support for --arch=x86_mscoff for LDC (for DMD compatibility)

dub.compilers.ldc: Fix --rdmd with --compiler=ldc2 ...

Use two dashes to make rdmd ignore the option. ldc2 doesn't care.

Add support for '-platformlib' option. Fixes #2031 ...

This change adds the newly introduced LDC linker option '-platformlib'
to the isLinkeDFlag(...) function in ldc.d so the option to be passed to
LDC when invoked by DUB for linking.

Replace occurences of 'in ref' with 'const scope ref' ...

In support for dlang/dmd#11000

ldc: support --arch=aarch64 and powerpc64 ...

Because Meson calls e.g. `dub describe something --arch aarch64`

LDC: Fix isLinkerDFlag() detection for options specified with 2 leading hyphens

Add support for iOS/tvOS/watchOS

[dip1000] Fix compilation and test it on Travis CI

Improve cross-compilation support (replace `version` checks by BuildPlatform runtime checks) ...

Also fixes #1249. For LDC as implicit cross compiler, the file
extensions for libraries and object files etc. don't depend on the
compiler, but solely on the target. Targets selected with `--arch` are
correctly probed by dub, so that the parsed `BuildPlatform` represents
the target platform.

ldc2: Only use `-L--no-as-needed` for Linux *targets*