PR28834, PR26946 sanity checking section size

PR28834, PR26946 sanity checking section size

This patch provides a new function to sanity check section sizes.
It's mostly extracted from what we had in bfd_get_full_section_contents
but also handles compressed debug sections.
Improvements are:
- section file offset is taken into account,
- added checks that a compressed section can be read from file.

The function is then used when handling multiple .debug_* sections
that need to be read into a single buffer, to sanity check sizes
before allocating the buffer.

	PR 26946, PR 28834
	* Makefile.am (LIBBFD_H_FILES): Add section.c.
	* compress.c (bfd_get_full_section_contents): Move section size
	sanity checks..
	* section.c (_bfd_section_size_insane): ..to here.  New function.
	* dwarf2.c (read_section): Use _bfd_section_size_insane.
	(_bfd_dwarf2_slurp_debug_info): Likewise.
	* Makefile.in: Regenerate.
	* libbfd.h: Regenerate.