symbol: add elf_section_by_name() helper (based on linux/perf/symbol-elf.c)

Add a helper for searching section in elf by it name.
Drop from original unused arguments, and variables.

Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>
symbol: add helpers for sdt probes.

Next helpers was added:
- search_stapsdt_note()
- sdt_note_data()
- sdt_note_name()
- sdt_note_addr()

Based on this patch set: https://lkml.org/lkml/2013/10/23/10

Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>
stapsdt: initial support for probing sdt notes.

For parsing ktap scripts, uprobes functions are used for stapsdt probes
too, the only differ between then is type argument, which is bypassed up
to find_symbol() that's it.

Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>
scripts: add test script for stapsdt probes

The only library in /lib/x86_64-linux-gnu that have sdt notes is
libgcc_s on by machine, with unwind marker.
So this patch add a simple ktap script that use it.

Signed-off-by: Azat Khuzhin <a3at.mail@gmail.com>