Move 4 libdwfl nested functions.

Move 4 libdwfl nested functions.

Now they should compile with clang.

Used local variables are passed to new file scope functions
as constant parameters, or pointers, or embedded in a
'state' structure.

One simple function "report" is changed to a macro.
It triggers a gcc false positive -Werror=maybe-uninitialized,
so the local variables are explicitly initialized.

Signed-off-by: Chih-Hung Hsieh <chh@google.com>