after "scons boost=0" fails, then "scons --help" fails with SSL library not found

$ scons boost=0
(build error)

stewart@willster:~/galera/galera2$ scons --help
scons: Reading SConscript files ...
Host: linux x86_64
Target: linux x86_64
Checking for C library pthread... (cached) yes
Checking for C library rt... (cached) yes
Checking for C header file sys/epoll.h... (cached) yes
Checking for C header file byteswap.h... (cached) yes
Checking for C header file endian.h... (cached) yes
Checking for C header file sys/endian.h... (cached) no
Checking for C++ header file boost/shared_ptr.hpp... (cached) yes
Checking for C++ header file boost/unordered_map.hpp... (cached) yes
Checking for C++ header file boost/pool/pool_alloc.hpp... yes
Using boost pool alloc
Checking for C++ header file asio.hpp... yes
Checking for C++ header file asio/ssl.hpp... yes
Checking for C library ssl... yes
Checking for C header file check.h... yes
Checking for C library check... yes
Checking for C++ library boost_program_options... (cached) yes
scons: done reading SConscript files.

Build targets: build tests check install all
Default target: all

Commandline Options:
    debug=n debug build with optimization level n
    arch=str target architecture [i686|x86_64]
    build_dir=dir build directory, default .
    boost=[0|1] disable or enable boost libraries
    revno=XXXX source code revision number

Use scons -H for help about command-line options.
stewart@willster:~/galera/galera2$ scons boost=0
scons: Reading SConscript files ...
Host: linux x86_64
Target: linux x86_64
Checking for C library pthread... (cached) yes
Checking for C library rt... (cached) yes
Checking for C header file sys/epoll.h... (cached) yes
Checking for C header file byteswap.h... (cached) yes
Checking for C header file endian.h... (cached) yes
Checking for C header file sys/endian.h... (cached) no
Checking for C++ header file boost/shared_ptr.hpp... (cached) yes
Checking for C++ header file boost/unordered_map.hpp... (cached) yes
Not using boost
Checking for C++ header file asio.hpp... yes
Checking for C++ header file asio/ssl.hpp... yes
Checking for C library ssl... no
ssl support required but openssl library not found
compile with ssl=0 or check that openssl library is usable