ld: Fix calls to strchr that discard or use wrong const qualifiers

* ld/emultempl/pe.em (pe_fixup_stdcalls): Make at a const char *.
	(gldEMULATION_NAME_after_open): Make pnt a const char *.
	(gldEMULATION_NAME_place_orphan): Make dollar a const char *.
	* ld/emultempl/pep.em (pep_fixup_stdcalls): Make at a
	const char *. Introduce at2 as non-const char *.
	(gldEMULATION_NAME_after_open): Make pnt a const char *.
	(gldEMULATION_NAME_place_orphan): Make dollar a const char *.
	* ld/emultempl/spuelf.em (spu_elf_load_ovl_mgr): Make p a
	const char *. Introduce np as char *.
	* ld/ldelf.c (ldelf_search_needed): Call strchr on freeme, so
	slash is non-const, then assign freeme to replacement.