hook-functions: copy_exec: Copy libgcc_s.so.0 along with libpthread.so

pthread_cancel() in libpthread.so.1 depends on functions in
libgcc_s.so.0, but uses dlopen() to link to it rather than having a
static dependency.  Handle this dynamic dependency in copy_exec so
that it doesn't have to be handled in every affected hook script.

Closes: #950254
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>