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

Fix misplaced closing bracket.

Fixed issue where static libraries would be generated instead of object files in singleFile build mode ...

+ Added object TargetType that is used during singleFile build mode

fixup #506 ...

- only use absolute initialCompilerBinary paths
- don't try to find absolute initialCompilerBinary in
  PATH

Fix: dub broken if compiled with absolute path DC ...

Code that was supposed to find working compiler always tried to
build absolute path from compiler name - even it was absolute
path already.

Use unique filenames for temporary files ...

Partial fix to #482

fix Issue 480 - default to available compiler ...

- search PATH for available compilers
- still prefer initialCompilerBinary (the one dub was build with)

Various small fixes ...

- fix computeBuildID for --compiler=/my/path;
- dub compiled with ldc tried to invoke ldc as default binary instead of ldc2;
- dmd: Don't generate anything;
- gdc: Do not link, only generate an object;