Silence gcc-8 warnings

Silence gcc-8 warnings

All of these warnings were false positives.  -Wstringop-truncation is
particularly annoying when it warns about strncpy used quite correctly.

bfd/
	* elf-linux-core.h (swap_linux_prpsinfo32_ugid32_out): Disable
	gcc-8 string truncation warning.
	(swap_linux_prpsinfo32_ugid16_out): Likewise.
	(swap_linux_prpsinfo64_ugid32_out): Likewise.
	(swap_linux_prpsinfo64_ugid16_out): Likewise.
	* elf.c (elfcore_write_prpsinfo): Likewise.
gas/
	* stabs.c (generate_asm_file): Use memcpy rather than strncpy.
	Remove call to strlen inside loop.
	* config/tc-cr16.c (getreg_image): Warning fix.
	* config/tc-crx.c (getreg_image): Warning fix.