gdb: update is_addr_in_objfile to support "dynamic" objfiles

gdb: update is_addr_in_objfile to support "dynamic" objfiles

While working with objfiles in Python I noticed that
gdb.Progspace.objfile_for_address () does not return "dynamic" objfile
create by (for example) GDB's JIT reader API.

This is because is_addr_in_objfile() checks if given address falls into
any (mappped) section of that objfile. However objfiles created by JIT
reader API do not have sections.

To solve this issue, this commit updates is_addr_in_objfile() to also
check if address fall into any compunit if that objfile. It does so only
if objfile has no sections.