Properly convert address load of __start_XXX/__stop_XXX

Properly convert address load of __start_XXX/__stop_XXX

Since __start_XXX and __stop_XXX symbols aren't defined when address
load is being converted, we need to check if there is an XXX output
section to get their section and value.  This patch adds a new function,
bfd_link_get_defined_symbol, to search for the XXX output section to
check if __start_XXX and __stop_XXX symbols are defined.

bfd/

	PR ld/19171
	* elf32-i386.c (elf_i386_convert_load): Call
	bfd_link_get_defined_symbol to check if a symbol is defined.
	* elf64-x86-64.c (elf_x86_64_convert_load): Call
	bfd_link_get_defined_symbol to get defined symbol section and
	value.
	* linker.c (bfd_link_get_defined_symbol): New function.
	* bfd-in2.h: Regenerated.

ld/testsuite/

	PR ld/19171
	* ld-i386/lea1.s: Add tests for address load of __start_XXX
	and __stop_XXX.
	* ld-i386/mov1.s: Likewise.
	* ld-x86-64/lea1.s: Likewise.
	* ld-x86-64/mov1.s: Likewise.
	* ld-i386/lea1a.d: Updated.
	* ld-i386/lea1b.d: Likewise.
	* ld-i386/lea1c.d: Likewise.
	* ld-i386/mov1a.d: Likewise.
	* ld-i386/mov1b.d: Likewise.
	* ld-x86-64/lea1a.d: Likewise.
	* ld-x86-64/lea1b.d: Likewise.
	* ld-x86-64/lea1c.d: Likewise.
	* ld-x86-64/lea1d.d: Likewise.
	* ld-x86-64/lea1e.d: Likewise.
	* ld-x86-64/lea1f.d: Likewise.
	* ld-x86-64/mov1a.d: Likewise.
	* ld-x86-64/mov1b.d: Likewise.
	* ld-x86-64/mov1c.d: Likewise.
	* ld-x86-64/mov1d.d: Likewise.