Silence uninitialized warning on ehdr_start_save

Older GCC, like 4.1/4.2, will issue an uninitialized warning on
ehdr_start_save.  This patch silences by using

struct bfd_link_hash_entry ehdr_start_save = ehdr_start_save;

	* emultempl/elf32.em (gld${EMULATION_NAME}_before_allocation):
	Silence uninitialized warning on ehdr_start_save with older
	GCC.