Fix compile time warning messages building with gcc v6.1.1

Fix compile time warning messages building with gcc v6.1.1

etc	* texi2pod.pl: Escape curly braces, whilst searching for keyword
	strong.

gas	* config/tc-arm.c: For non-ELF based targets skip ARM feature sets
	that are not supported.

	* config/tc-arc.c (md_apply_fix): Avoid left shifting a signed
	constant.
	* config/tc-cr16.c (check_range): Likewise.
	* config/tc-nios2.c (nios2_check_overflow): Likewise.