LD: Convert `%P: %H:' to `%H:' in error messages

LD: Convert `%P: %H:' to `%H:' in error messages

Similarly to commit 174d0a74a2e6 ("PowerPC/BFD: Convert `%P: %H:' to
`%H:' in error messages") convert linker relocation error messages to
use `%H:' rather `%P: %H:', removing inconsistent message composition
like:

$ cat reloc-j.s
	.text
	.globl	foo
	.ent	foo
foo:
	j	bar
	j	bar
	.end	foo
$ cat reloc-j.ld
SECTIONS
{
  bar = 0x12345678;
  .text : { *(.text) }
  /DISCARD/ : { *(*) }
}
$ as -o reloc-j.o reloc-j.s
$ ld -T reloc-j.ld -o reloc-j reloc-j.o
ld: tmpdir/reloc-j.o: in function `foo':
(.text+0x0): relocation truncated to fit: R_MIPS_26 against `bar'
ld: (.text+0x8): relocation truncated to fit: R_MIPS_26 against `bar'
$

where subsequent lines referring to issues within a single function have
the name of the linker executable prepended, but the first one does not.

As noted with the commit referred this breaks a GNU Coding Standard's
requirement that error messages from compilers should look like this:

source-file-name:lineno: message

also quoted in `vfinfo' code handling these specifiers.

Remove the linker name prefix then, making the messages now look like:

$ ld -T reloc-j.ld -o reloc-j reloc-j.o
tmpdir/reloc-j.o: in function `foo':
(.text+0x0): relocation truncated to fit: R_MIPS_26 against `bar'
(.text+0x8): relocation truncated to fit: R_MIPS_26 against `bar'
$

instead.

	ld/
	* ldmain.c (reloc_overflow): Use `%H:' rather than `%P: %H:'
	with `einfo'.
	(reloc_dangerous): Likewise.
	(unattached_reloc): Likewise.