Build the MariaODBC driver as a module

[AdamMajer]

When built as a module instead of a shared library, the library is
no longer exporting an unversioned soname. Since this is library is
only meant to be dynamically loaded by the ODBC manager, the soname
is unused anyway.

objdump -x libmaodbc.so | grep SONAME

[lawrinn]

Some people do link against odbc drivers directly to remove overhead introduced by a DM. Thus I don't want to remove SONAME export and inclined to reject this PR.

[AdamMajer]

Hmmm, my instinct tells me that soname-less libraries have implicit "soname" equal to their filename. The soname is only used to write a different filename into the executable header than the filename from the linker. And I've just verified this. For example, a very simply test that uses a symbol from the library (wrongly, of course),

extern void SQLTables();

int main()
{
SQLTables();
return 0;
}

Will link with the library without explicit soname.

objdump -x a.out | grep NEEDED
  NEEDED               libmaodbc.so
  NEEDED               libc.so.6

So my commit message is incorrect. The explicit soname set to the filename (unversioned) is superfluous and unnecessary in all use-cases. You can also see this in the manpage of ld(1)

   -h name
   -soname=name
       When creating an ELF shared object, set the internal DT_SONAME field to the specified name.  
       When an executable is linked with a shared object which has a DT_SONAME field,
       then when the executable is run the dynamic linker will attempt to load the shared object specified 
       by the DT_SONAME field rather than the using the file name given to the linker.

[AdamMajer]

I've corrected the commit message. For our packaging, the presence of a soname breaks some automatic packaging checks.