Skip PLT for function pointer initialization

Skip PLT for function pointer initialization

We use its PLT entry to initialize function pointer at run-time.  If
there is no other usage for the PLT entry, we can generate run-time
function pointer relocations in read-write section, which can be
resolved by dynamic linker, to initialize function pointers.  It avoids
the extra indirect branch overhead in PLT.

bfd/

	PR ld/18900
	* elf32-i386.c (elf_i386_link_hash_entry): Add
	func_pointer_refcount.
	(elf_i386_link_hash_newfunc): Clear func_pointer_refcount.
	(elf_i386_get_local_sym_hash): Likewise.
	(elf_i386_copy_indirect_symbol): Also copy
	func_pointer_refcount.
	(elf_i386_check_relocs): Increment func_pointer_refcount.
	(elf_i386_gc_sweep_hook): Decrement func_pointer_refcount.
	(elf_i386_allocate_dynrelocs): Don't create the PLT entry if
	there are only function pointer relocations which can be
	resolved at run-time.  Keep dynanamic relocations for run-time
	function pointer initialization.
	(elf_i386_relocate_section): Copy dynamic function pointer
	relocations.
	* elf64-x86-64.c (elf_x86_64_link_hash_entry): Add
	func_pointer_refcount.
	(elf_x86_64_link_hash_newfunc): Clear func_pointer_refcount.
	(elf_x86_64_get_local_sym_hash): Likewise.
	(elf_x86_64_copy_indirect_symbol): Also copy
	func_pointer_refcount.
	(elf_x86_64_check_relocs): Increment func_pointer_refcount.
	(elf_x86_64_gc_sweep_hook): Decrement func_pointer_refcount.
	(elf_x86_64_allocate_dynrelocs): Don't create the PLT entry if
	there are only function pointer relocations which can be
	resolved at run-time.  Keep dynanamic relocations for run-time
	function pointer initialization.
	(elf_x86_64_relocate_section): Copy dynamic function pointer
	relocations.

ld/testsuite/

	PR ld/18900
	* ld-i386/i386.exp: Run tests for PR ld/18900.
	* ld-x86-64/x86-64.exp: Likewise.
	* ld-i386/pr18900.out: New file.
	* ld-i386/pr18900a.c: Likewise.
	* ld-i386/pr18900a.c: Likewise.
	* ld-i386/pr18900a.rd: Likewise.
	* ld-i386/pr18900b.c: Likewise.
	* ld-i386/pr18900b.rd: Likewise.
	* ld-i386/pr18900c.c: Likewise.
	* ld-x86-64/pr18900.out: Likewise.
	* ld-x86-64/pr18900a.c: Likewise.
	* ld-x86-64/pr18900a.rd: Likewise.
	* ld-x86-64/pr18900b.c: Likewise.
	* ld-x86-64/pr18900b.rd: Likewise.
	* ld-x86-64/pr18900c.c: Likewise.
	* ld-x86-64/mpx3.dd: Updated.