4.10.0

This release contains many bug fixes but along the way also cleanup and
refactoring of many toolsets, thanks to Nikita.

• New: Scan assembler files for C Preprocessor includes.
  -- Nikita Kniazev
• Fix: Inherit generator overrides from a base toolset.
  -- Nikita Kniazev
• New: Add linemarkers feature that on preprocessing targets changes behavior to
  emit/omit line directives like #line and #<linenum>.
  -- Nikita Kniazev
• Fix compiler name for QNX.
  -- James Choi
• Fix openssl name handling.
  -- Dmitry Arkhipov
• Fix clang-win assembler path deduction.
  -- Nikita Kniazev
• Fix toolset sub-feature requirements inheritance.
  -- Nikita Kniazev
• Unify compile and link of clang-linux toolset with gcc toolset.
  -- Nikita Kniazev
• Fix same directory pch header generation for msvc toolset.
  -- Nikita Kniazev
• Implement --durations which reports top targets by execution time.
  -- Nikita Kniazev
• Change clang-darwin to inherit from clang-linux and unify compile commands.
  -- Nikita Kniazev
• Fix clang-linux to not override RPATH_OPTION.
  -- Nikita Kniazev
• Fix inadvertently running configuration checks that shouldn't (as reported by
  Alexander Grund). By changing <build>no conditionals evaluation to short
  circuit.
  -- Nikita Kniazev
• Fix same toolset overrides (inherit-overrides).
  -- Nikita Kniazev
• New: Add using the C processors for assembly source files.
  -- Nikita Kniazev
• Many improvements and cleanup of internal testing.
  -- Nikita Kniazev
• Unify gcc and clang-linux soname option handling and disable it on Windows.
  -- Nikita Kniazev
• Unity gcc/mingw linking of shared and import libs.
  -- Nikita Kniazev
• Fix pdb generation ordering and naming issues.
  -- Nikita Kniazev
• Unify clang-darwin linking with gcc.
  -- Nikita Kniazev
• Fix mingw/msys/cygwin, winthreads/pthread inconsistencies to correct compiler
  flags.
  -- Nikita Kniazev
• Unify clang-vxworks by inheriting from clang-linux.
  -- Nikita Kniazev
• Don't store empty config cache and log.
  -- Nikita Kniazev
• Fix generator custom rule name inheritance. This affects cygwin/mingw linking.
  -- Nikita Kniazev
• Fix testing.execute=off to correct run-fail behavior.
  -- Nikita Kniazev
• Fix use-project with native paths.
  -- René Ferdinand Rivera Morell
• Fix msvc auto config version priority. Now msvc toolsets are configured in
  correct newest to oldest regardless of being found from the registry or not.
  -- René Ferdinand Rivera Morell
• New: Add support for automatic searching of external projects for global
  target and project references.
  -- René Ferdinand Rivera Morell