build error with boost 1.68

When building boost 1.68, I have an error when building program_options where it cannot copy the program_options-mt.lib file.

It seems the .lib file is not created since nothing is exported when not using `BOOST_ALL_DYN_LIB`.

Taking example on boost.timer, I modified the Jamfile.v2 file to look like this
```
boost-lib program_options
: $(SOURCES).cpp
: # See https://svn.boost.org/trac/boost/ticket/5049
hpux,gcc:_INCLUDE_STDC__SOURCE_199901
shared:BOOST_PROGRAM_OPTIONS_DYN_LINK=1
static:BOOST_PROGRAM_OPTIONS_STATIC_LINK=1
;
```

and it seems to fix my issue.

Comienza con el program_options Jamfile.v2 y compara su definición de boost-lib con el ejemplo de boost.timer mencionado en el issue. Reproduce la compilación de Boost 1.68 y verifica que se cree program_options-mt.lib y que se pueda copiar correctamente.

Escrito por el modelo de indexación a partir del texto del issue.