PR23595, simple objcopy of executable failure for msp430-elf

PR23595, simple objcopy of executable failure for msp430-elf

VMA of the first section in the segment containing the ELF file header
(and possibly section headers too) can't be used to reliably find the
size of the headers plus padding.  What's really needed is sh_offset
of the first section assuming it has contents (vma does have a
relationship to sh_offset, but is only guaranteed in demand paged
executables).

If the first section is SHT_NOBITS and it hasn't been converted to
have file contents by the existence of a following SHT_PROGBITS
section in the same segment, the sh_offset value also isn't reliable.

	PR 23595
	elf.c (copy_elf_program_header): When first segment contains
	only the headers and SHT_NOBITS sections, use segment p_filesz
	to calculate header and padding size.  Use filepos of the first
	section otherwise.