Hi,

I attach a patch to enable -fvisibility=hidden whenever compiler supports it. This allowed me to remove several private symbols from gdbm slibs. Removing private symbols has several benefits (allowing compiler to do more aggressive optimizations, speeding up dynamic linker startup, preventing clients from using library internals) so perhaps something like this could be merged to trunk?

List of removed symbols:
_gdbm_alloc
_gdbm_base64_decode
_gdbm_base64_encode
_gdbm_bucket_dir
_gdbm_dump_ascii
_gdbm_end_update
_gdbm_fatal
_gdbm_file
_gdbm_file_size
_gdbm_findkey
_gdbm_free
_gdbm_full_write
_gdbm_init_cache
_gdbm_internal_remap
gdbm_load_bdb_dump
_gdbm_load_file
_gdbm_lock_file
_gdbm_mapped_init
_gdbm_mapped_read
_gdbm_mapped_remap
_gdbm_mapped_sync
_gdbm_mapped_unmap
_gdbm_mapped_write
_gdbm_new_bucket
_gdbm_next_bucket_dir
_gdbm_put_av_elem
_gdbm_read_bucket_at
_gdbm_read_entry
_gdbm_split_bucket
_gdbm_unlock_file
_gdbm_write_bucket
get_len
read_record

The issue was detected via https://github.com/yugr/ShlibVisibilityChecker