perf machine: Set PROT_EXEC for executable PERF_RECORD_MMAP records

perf machine: Set PROT_EXEC for executable PERF_RECORD_MMAP records

The kernel doesn't fill the map 'prot' field for PERF_RECORD_MMAP
records, and we will use that info to replace checking for
MAP__VARIABLE, so store that when processing the
PERF_RECORD_MISC_MMAP_DATA perf_event_attr.header.misc bit.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-es3zz9r0q2qlssg4wh1w1d8p@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>