Log Message:
scons: updated to 3.1.2

RELEASE 3.1.2:
- Added debug option "action_timestamps" which outputs to stdout the \ 
absolute start and end time for each target.
- Fix suncxx tool (Oracle Studio compiler) when using Python 3.  Previously \ 
would throw an exception.
  Resolved by properly handling tool version string output as unicode.
- Resolved a typo in engine.SCons.Tool
- Resolved a race condition in multithreaded Windows builds with Python 2
  in the case where a child process is spawned while a Python action has a
  file open. Original author: Ryan Beasley.
- Update Command() function to accept target_scanner, source_factory, and \ 
target_factory arguments.
  This makes Command act more like a one-off builder.
- Added support for "-imacros" to ParseFlags
- Fix CheckFunc detection code for Visual 2019. Some functions
  (e.g. memmove) were incorrectly recognized as not available.
- Fix stacktrace when using SCons with Python 3.5+ and SunOS/Solaris related tools.
- Avoid crash with UnicodeDecodeError on Python 3 when a Latex log file in
  non-UTF-8 encoding (e.g. containing umlauts in Latin-1 encoding when
  the fontenc package is included with \usepackage[T1]{fontenc}) is read.
- Improved threading performance by ensuring NodeInfo is shared
  across threads. Results in ~13% improvement for parallel builds
  (-j# > 1) with many shared nodes.
- Improve performance of Entry.disambiguate() by making check for
  most common case first, preventing unnecessary IO.
- Improved DAG walk performance by reducing unnecessary work when
  there are no un-visited children.
- Replace instances of string find method with "in" checks where
  the index from find() was not used.
- CmdStringHolder fix from issue 3428
- Turn previously deprecated debug options into failures:
  --debug=tree, --debug=dtree, --debug=stree, --debug=nomemoizer.
- Experimental New Feature: Enable caching MSVC configuration
  If SCONS_CACHE_MSVC_CONFIG shell environment variable is set,
  SCons will cache the results of past calls to vcvarsall.bat to
  a file; integrates with existing memoizing of such vars.
  On vs2019 saves 5+ seconds per SCons invocation, which really
  helps test suite runs.
- Remove deprecated SourceSignatures, TargetSignatures
- Remove deprecated Builder keywords: overrides and scanner
- Remove deprecated env.Copy
- Remove deprecated BuildDir plus SConscript keyword build_dir
- A number of documentation improvements.