LDC: Suppress noisy warning when cross-compiling via -arch=<triple>

Fix #1206: Remove warning when using ldmd2 or gdmd ...

This warning is being triggered frequently when ldmd2 or gdmd
(dmd-like CLI interface for ldc2 and gdc, respectively)
are used as '--compiler' argument.
They were introduced at the same time as the platform probe
(8ac4848),
probably for defensive programming, but have not proved useful.

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.

Use -dumpfullversion to determine GDC version

Perform the tool chain checks based on the compiler name. ...

Gets rid of the additional methods in the Compiler interface and moves the checks to a more central location, since other generators apart from BuildGenerator might want to perform the checks in the future. Also keeps the API "package" for now to avoid adding insufficiently though-out public APIs.

Change toolchainRequirements fields to Dependency. ...

Also removes some API clutter from Compiler and PackageRecipe.

Remove the additional '|' syntax for toolchain requirements. ...

- '|' seems confusing, given that it is used as a logical AND
- Dependency already supports specifying an arbitrary range and this is the only meaningful use for '|'
- Keeps the possibility open to use '|' as a logical OR in a later version
- Rewords the change log entry and adds a link to the DUB documentation

toolchainRequirements recipe support

Also fix x86_mscoff to be available as a platform specifier. See #1059.

Merge pull request #1059 from MrSmith33/master ...

Fix 'Failed to apply the selected architecture x86_mscoff. Got ["x86"]' when passing --arch=x86_mscoff
(cherry picked from commit 2039b93)

dmd, gdc: move common platform detection code to the base interface.

Merge pull request #688 from dlang/fix_issue_618 ...

Fix library extensions for LDC when using the MS linker. Fixes #618.

Remove deprecated functionality to prepare for 1.0.0.

Move getTargetFileName to Compiler interface. ...

See #618.

Deprecate dub.compilers.compiler.defaultCompiler and improve docs. ...

Merges the code from compiler.defaultCompiler into the Dub class.

Improves documentation comment for Dub.defaultCompiler.

Move compiler registration code from to dub.dub. ...

Breaks the import cycle between dub.compilers.compiler and dub.compilers.ldc/gdc/dmd.

Add documentation for dub.compilers.compiler/utils.

Move utility functions from dub.compilers.compiler to dub.compilers.utils.

Fix naming convention for the compiler handler classes and add documentation.

Move BuildPlatform to dub.platform and improve docs.

Fix for issue #782. Analyze the output of pkg-config --libs <lib> and massage them if they appear to already be ready for direct use with the compiler. ...

This change allows using pkg-config within dub with .pc files that were written for use with the compiler directly, which can prove troublesome in some cases (for instance, when using the GtkD debian packages as mentioned in issue #7
82).
Basically, we analyze the output of pkg-config and fix up arguments so that they are suitable for the D compiler invokations through dub.

Arguments handled include:
- double "-L" flags (from gtkd3.pc for example) -> passed as single "-L" flags
- "-defaultlib" flags (from phobos2.pc for example) -> passed as-is (previous dub code used to pass them as "-Ldefaultlib")
- "-pthread" flags (from libavcode.pc for example) -> passed as "-L-l-pthread" (previous dub code used to pass them as-is)

The test case tests for these arguments explicitly, is currently only applicable to DMD frontend versions >= 2.068 as other frontends/versions seems to have some issues with shared libraries.

Merge pull request #679 from Abscissa/fix624 ...

Fix #624: --data=libs should output in compiler-format, not linker fo…

The default compiler should not depend on DUB's own build environment

Fix #624: --data=libs should output in compiler-format, not linker format.

Improve error message for invalid platform specifications. ...

Actually this enforcement could be an assertion instead, as there should be no way to trigger it from the outside...

Fix naming convention of FileMode enum. ...

Also some minor code style fixes.

Change Build(Options/Requirements) to BitFlags.

replace for loops and additional filtering with partition

Support packages without "lib" prefix in pkg-config ...

This fixes #300.

Fixed typo in compilers/compiler.d