tools build: Add capability-related feature detection

Add utilities to help checking capabilities of the running procss.  Make
perf link with libcap, if it is available. If no libcap-dev[el], assume
no capabilities.

Committer testing:

  $ make O=/tmp/build/perf -C tools/perf install-bin
  make: Entering directory '/home/acme/git/perf/tools/perf'
    BUILD:   Doing 'make -j8' parallel build

  Auto-detecting system features:
  <SNIP>
  ...                        libbfd: [ on  ]
  ...                        libcap: [ OFF ]
  ...                        libelf: [ on  ]
  <SNIP>
  Makefile.config:833: No libcap found, disables capability support, please install libcap-devel/libcap-dev
  <SNIP>
  $ grep libcap /tmp/build/perf/FEATURE-DUMP
  feature-libcap=0
  $ cat /tmp/build/perf/feature/test-libcap.make.output
  test-libcap.c:2:10: fatal error: sys/capability.h: No such file or directory
      2 | #include <sys/capability.h>
        |          ^~~~~~~~~~~~~~~~~~
  compilation terminated.
  $

Now install li...