Rename lang_output_section_statement to lang_os_list

Rename lang_output_section_statement to lang_os_list

The idea is to make it a little easier to find uses of this list,
so searches don't hit occurrences of lang_output_section_statement_type
and lang_output_section_statement_enum.

	* ldlang.h (lang_os_list): Rename from lang_output_section_statement.
	* ldlang.c: Likewise throughout file.
	* emultempl/alphaelf.em: Likewise.
	* emultempl/elf32.em: Likewise.
	* emultempl/mmo.em: Likewise.
	* emultempl/pe.em: Likewise.
	* emultempl/pep.em: Likewise.
	* emultempl/ppc32elf.em: Likewise.
	* emultempl/spuelf.em: Likewise.