Adjust bootstrap for current B2 builds.

These are some minor adjustments to the bootstrap step of building B2. For bootstrap.bat we no longer shove B2 build output to the bootstrap.log file as we want to see the helpful diagnostic messages from B2. For example, indicating the requirement of C++11 for the engine build. This also renames from Boost.Build to B2. And adds clang as an option for bootstrap config creation.

bootstrap.bat

@@ -2,7 +2,7 @@
 
 SETLOCAL
 
-REM Copyright 2019 Rene Rivera
+REM Copyright 2019-2020 Rene Rivera
 REM Copyright (C) 2009 Vladimir Prus
 REM
 REM Distributed under the Boost Software License, Version 1.0.
@@ -12,7 +12,7 @@ ECHO Building Boost.Build engine
 if exist ".\tools\build\src\engine\b2.exe" del tools\build\src\engine\b2.exe
 pushd tools\build\src\engine
 
-call .\build.bat %* > ..\..\..\..\bootstrap.log
+call .\build.bat
 @ECHO OFF
 
 popd
@@ -33,6 +33,7 @@ REM properly. Default to msvc if not specified.
 SET TOOLSET=msvc
 
 IF "%1"=="gcc" SET TOOLSET=gcc
+IF "%1"=="clang" SET TOOLSET=clang
 
 IF "%1"=="vc71" SET TOOLSET=msvc : 7.1
 IF "%1"=="vc8" SET TOOLSET=msvc : 8.0
@@ -88,7 +89,6 @@ goto :end
 
 ECHO.
 ECHO Failed to build Boost.Build engine.
-ECHO Please consult bootstrap.log for further diagnostics.
 ECHO.
 
 REM Set an error code to allow `bootstrap && b2`