libexecinfo: Enable backtrace_test.backtrace_fmt_basic on amd64 again

Due to unwind tables generation enabled after c969310c for csu.

PR: 241562, 246322, 246537
Reviewed by: kib, ngie
Differential Revision: https://reviews.freebsd.org/D40758

Temporarily disable failing case in CI of amd64:

- lib.libexecinfo.backtrace_test.backtrace_fmt_basic

PR: 246537
Sponsored by: The FreeBSD Foundation

Revert r354238 as the issue has been fixed in r354418

PR: 241562
Sponsored by: The FreeBSD Foundation

Temporarily skip lib.libexecinfo.backtrace_test.backtrace_fmt_basic on i386

PR: 241562
Sponsored by: The FreeBSD Foundation

libexecinfo test: Don't strip installed test

It turns out that a test of backtrace symbol resolution and formatting
requires symbols. Another option mightt be building with -rdynamic instead,
but this works for now.

Re-enabled skipped CI test, as it should now pass.

PR: 241562
Submitted by: lwhsu
Reported by: lwhsu
X-MFC-With: r354126, r354135, r354144

Temporarily disable failing case in CI:

- lib.libexecinfo.backtrace_test.backtrace_fmt_basic

PR: 241562
Sponsored by: The FreeBSD Foundation

Remove bogus requirement from libexecinfo test

The bogus requirement was causing CI infrastructure (which does not mount
procfs) to skip the test. Procfs has not been needed by libexecinfo on
FreeBSD (nor NetBSD) for years. Both now use a sysctl to obtain the path to
the current process image.

X-MFC-With: r354126

Import proper fix for misc/49356 (/usr/include/atf-c/config.h) after atf-c/config.h
was removed from the build

Pointyhat to: me (again, for not running make delete-old after running test builds)