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 libcap-devel and try again:

  $ 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
  Warning: Kernel ABI header at 'tools/include/linux/bits.h' differs from latest version at 'include/linux/bits.h'
  diff -u tools/include/linux/bits.h include/linux/bits.h
  Warning: Kernel ABI header at 'tools/arch/x86/include/asm/cpufeatures.h' differs from latest version at 'arch/x86/include/asm/cpufeatures.h'
  diff -u tools/arch/x86/include/asm/cpufeatures.h arch/x86/include/asm/cpufeatures.h

  Auto-detecting system features:
  <SNIP>
  ...                        libbfd: [ on  ]
  ...                        libcap: [ on  ]
  ...                        libelf: [ on  ]
  <SNIP>>
    CC       /tmp/build/perf/jvmti/libjvmti.o
  <SNIP>>
  $ grep libcap /tmp/build/perf/FEATURE-DUMP
  feature-libcap=1
  $ cat /tmp/build/perf/feature/test-libcap.make.output
  $ ldd /tmp/build/perf/feature/test-libcap.make.bin
  ldd: /tmp/build/perf/feature/test-libcap.make.bin: No such file or directory
  $ ldd /tmp/build/perf/feature/test-libcap.bin
  	linux-vdso.so.1 (0x00007ffc35bfe000)
  	libcap.so.2 => /lib64/libcap.so.2 (0x00007ff9c62ff000)
  	libc.so.6 => /lib64/libc.so.6 (0x00007ff9c6139000)
  	/lib64/ld-linux-x86-64.so.2 (0x00007ff9c6326000)
  $

Signed-off-by: Igor Lubashev <ilubashe@akamai.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
[ split from a larger patch ]
Link: http://lkml.kernel.org/r/8a1e76cf5c7c9796d0d4d240fbaa85305298aafa.1565188228.git.ilubashe@akamai.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>