Properly check symbol defined by assignment in linker script

Properly check symbol defined by assignment in linker script

Symbol defined by a linker assignment may have type bfd_link_hash_new
or bfd_link_hash_undefined.  And h->def_regular is always set.
elf_i386_convert_load and elf_x86_64_convert_load should check
h->def_regular as well as bfd_link_hash_undefined and bfd_link_hash_new
to see if a symbol is defined by a linker script.

bfd/

	PR ld/19319
	* elf32-i386.c (elf_i386_convert_load): Check h->def_regular
	instead of bfd_link_hash_new.
	* elf64-x86-64.c (elf_x86_64_convert_load): Likewise.  Skip
	relocation overflow for bfd_link_hash_undefined and
	bfd_link_hash_new if h->def_regular is set.

ld/testsuite/

	PR ld/19319
	* ld-i386/i386.exp: Run pr19319 test.
	* ld-x86-64/x86-64.exp: Likewise.
	* ld-i386/pr19319.dd: New file.
	* ld-i386/pr19319a.S: Likewise.
	* ld-i386/pr19319b.S: Likewise.
	* ld-x86-64/pr19319.dd: Likewise.
	* ld-x86-64/pr19319a.S: Likewise.
	* ld-x86-64/pr19319b.S: Likewise.

(cherry picked from commit ead3d5427a2df5e33316d4ad045510c1d2078c2a)