Add command line option to stop the assembler from padding the end of sections to...

Add command line option to stop the assembler from padding the end of sections to their alignment boundary.

	PR gas/20247
	* as.h (do_not_pad_sections_to_alignment): New global variable.
	* as.c (show_usage): Add --no-pad-sections.
	(parse_args): Likewise.
	* write.c (size_seg): Skip padding the end of the section if
	requested from the command line.
	(SUB_SEGMENT_ALIGN): Likewise.
	* doc/as.texinfo: Document the new option.
	* NEWS: Mention the new feature.
	* testsuite/gas/elf/section11.s: New test.
	* testsuite/gas/elf/section11.d: New test driver.
	* testsuite/gas/elf/elf.exp: Run the new test.