Statically initialise target common sections

This tidies initialisation of target common sections, doing so using a
static initialiser rather than via code and deleting unnecessary
symbol_ptr_ptr variables (the one in asection is used instead).

The patch also initialises ecoff.c:bfd_debug_section using
BFD_FAKE_SECTION.  That does change bfd_debug_section slightly,
output_section was NULL now bfd_debug_section, and symbol_ptr_ptr
was NULL now &bfd_debug_section.symbol, but I believe those changes
are safe.

bfd/
	* ecoff.c (bfd_debug_section): Init using BFD_FAKE_SECTION.
	(ecoff_scom_section, ecoff_scom_symbol): Statically init using
	BFD_FAKE_SECTION and GLOBAL_SYM_INIT.  Delete initialisation code.
	(ecoff_scom_symbol_ptr): Delete.
	* elf32-m32r.c (m32r_elf_scom_section, m32r_elf_scom_symbol),
	(m32r_elf_scom_symbol_ptr),
	* elf32-score.c (score_elf_scom_section, score_elf_scom_symbol),
	(score_elf_scom_symbol_ptr),
	* elf32-score7.c (score_elf_scom_section, score_elf_scom_symbol),
	(score_elf_scom_sy...