readelf.c: Avoid repeating calls to gettext _() in hotpath

readelf.c: Avoid repeating calls to gettext _() in hotpath

Calls to the gettext _() macro in hotpaths cause many runtime lookups
of the same translation strings.  This patch introduces macro __()
which caches the result of _() at each call site where __() is used.

When a cached translation string is used as the format string for
fprintf, the compiler might raise a -Wformat-nonliteral warning.

To avoid this, the -Wformat-nonliteral warning is suppressed using _Pragma
around affected fprintf calls, using IGNORE_FMT_NONLITERAL_BEGIN and
_END wrappers.

To avoid suppressing -Wformat-nonliteral across every printf-style
function using _(), __() and IGNORE_FMT_NONLITERAL_* are mostly used
within hotpath loops where caching makes a signficant difference.
Runtime improvements of up to 13% faster have been observed with this patch
applied.

Signed-off-by: Aaron Merey <amerey@redhat.com>