Re: ld script expression parsing

Commit 40726f16a8d7 broke references to sections within ADDR(), and
overlays with weird section names.

	* ldgram.y (paren_script_name): New rule.
	(exp): Use it for ALIGNOF, SIZEOF, ADDR, and LOADADDR.  Similarly
	ensure script mode parsing for section name in SEGMENT_START.
	(overlay_section): Delete unnecessary ldlex_script call.  Backup
	on a lookahead NAME parsed in expression mode.
	* testsuite/ld-elf/overlay.s: Add more sections.
	* testsuite/ld-elf/overlay.t: Test '-' in section names.