selftests/bpf: Extend uprobe/uretprobe triggering benchmarks

Settle on three "flavors" of uprobe/uretprobe, installed on different
kinds of instruction: nop, push, and ret. All three are testing
different internal code paths emulating or single-stepping instructions,
so are interesting to compare and benchmark separately.

To ensure `push rbp` instruction we ensure that uprobe_target_push() is
not a leaf function by calling (global __weak) noop function and
returning something afterwards (if we don't do that, compiler will just
do a tail call optimization).

Also, we need to make sure that compiler isn't skipping frame pointer
generation, so let's add `-fno-omit-frame-pointers` to Makefile.

Just to give an idea of where we currently stand in terms of relative
performance of different uprobe/uretprobe cases vs a cheap syscall
(getpgid()) baseline, here are results from my local machine:

$ benchs/run_bench_uprobes.sh
base : 1.561 ± 0.020M/s
uprobe-nop : 0.947 ± 0.007M/s
uprobe-push : 0.951 ± 0.004M/s
uprobe-ret : 0.443 ± 0.007M/s
uretprobe-nop : 0.471 ± 0.013M/s
uretprobe-push : 0.483 ± 0.004M/s
uretprobe-ret : 0.306 ± 0.007M/s

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240301214551.1686095-1-andrii@kernel.org