readelf: print warning for -sW

The option -s accepts in elfutils (compared to binutils) a positional
argument that is name of a symbol table section which should be printed.

Thus, print a reasonable warning if -sW is used:
./src/readelf -sW a.out
WARNING: cannot find section: 'W'

PR29719

src/ChangeLog:

	* readelf.c (print_symtab): Change signature and return true if
	something is printed.
	(process_elf_file): Use it and print warning.

tests/ChangeLog:

	* run-readelf-s.sh: Test -sW.
2 files changed