benchmark

[bazel] Build libpfm as a dependency to allow collection of perf counters (#1408)

* Build libpfm as a dependency to allow collection of perf counters

This commit builds libpfm using rules_foreign_cc and lets the default
build of the benchmark library support perf counter collection without
needing additional work from users.

Tested with a custom target:

```
bazel run \
        --override_repository=com_github_google_benchmark=/home/raghu/benchmark \
        -c opt :test-bench -- "--benchmark_perf_counters=INSTRUCTIONS,CYCLES"
Using profile: local

<snip>

----------------------------------------------------------------------
Benchmark            Time             CPU   Iterations UserCounters...
----------------------------------------------------------------------
BM_Test      0.279 ns        0.279 ns   1000000000 CYCLES=1.00888 INSTRUCTIONS=2

```

Signed-off-by: Raghu Raja <raghu@enfabrica.net>

* Adding myself to the CONTRIBUTORS file per CLA guidance

Enfabrica has already signed a corporate CLA.

Signed-off-by: Raghu Raja <raghu@enfabrica.net>

Signed-off-by: Raghu Raja <raghu@enfabrica.net>