debuginfod: export DEBUGINFOD_SONAME macro in debuginfod.h

Add DEBUGINFOD_SONAME macro to API for use by those of libdebuginfod
clients that would like to dlopen the library in the same way as
__libdwfl_debuginfod_init does.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
7 files changed