The accepted answer is correct. Adding this in case somebody else googles this answer and still fails to produce x64 version.
Following is what I had to do to build Boost 1.63 on Visual Studio 15 2017 Community Edition.
Commands executed from VS environment cmd shell. Tools -> Visual Studio Command Prompt
C:\Work\Boost_1_63> C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat amd64
C:\Work\Boost_1_63> bootstrap.bat
C:\Work\Boost_1_63> bjam -j4 architecture=x86 address-model=64 link=static stage
C:\Work\Boost_1_63> bjam --prefix=C:\opt\boost architecture=x86 address-model=64 link=static install
You can verify that the resulting .lib is x64 with dumpbin:
C:\Work> dumpbin /headers C:\work\boost_1_63\stage\lib\libboost_locale-vc140-mt-1_63.lib | findstr machine
8664 machine (x64)
8664 machine (x64)
8664 machine (x64)
8664 machine (x64)
...
b2
. – Sinusitis