perf header: Pack 'struct perf_session_env'

Initial struct:

[acme@ssdandy linux]$ pahole -C perf_session_env ~/bin/perf
struct perf_session_env {
	char *                     hostname;             /*     0     8 */
	char *                     os_release;           /*     8     8 */
	char *                     version;              /*    16     8 */
	char *                     arch;                 /*    24     8 */
	int                        nr_cpus_online;       /*    32     4 */
	int                        nr_cpus_avail;        /*    36     4 */
	char *                     cpu_desc;             /*    40     8 */
	char *                     cpuid;                /*    48     8 */
	long long unsigned int     total_mem;            /*    56     8 */
	/* --- cacheline 1 boundary (64 bytes) --- */
	int                        nr_cmdline;           /*    64     4 */

	/* XXX 4 bytes hole, try to pack */

	char *                     cmdline;              /*    72     8 */
	int                        nr_sibling_cores;     /*    80     4 */

	/* XXX 4 bytes hole, try to pack */

	char *                     sibling_cores;        /*    88     8 */
	int                        nr_sibling_threads;   /*    96     4 */

	/* XXX 4 bytes hole, try to pack */

	char *                     sibling_threads;      /*   104     8 */
	int                        nr_numa_nodes;        /*   112     4 */

	/* XXX 4 bytes hole, try to pack */

	char *                     numa_nodes;           /*   120     8 */
	/* --- cacheline 2 boundary (128 bytes) --- */
	int                        nr_pmu_mappings;      /*   128     4 */

	/* XXX 4 bytes hole, try to pack */

	char *                     pmu_mappings;         /*   136     8 */
	int                        nr_groups;            /*   144     4 */

	/* size: 152, cachelines: 3, members: 20 */
	/* sum members: 128, holes: 5, sum holes: 20 */
	/* padding: 4 */
	/* last cacheline: 24 bytes */
};
[acme@ssdandy linux]$

[acme@ssdandy linux]$ pahole -C perf_session_env --reorganize --show_reorg_steps ~/bin/perf | grep ^/ | grep -v Final
/* Moving 'nr_sibling_cores' from after 'cmdline' to after 'nr_cmdline' */
/* Moving 'nr_numa_nodes' from after 'sibling_threads' to after 'nr_sibling_threads' */
/* Moving 'nr_groups' from after 'pmu_mappings' to after 'nr_pmu_mappings' */
[acme@ssdandy linux]$

Final struct stats:

[acme@ssdandy linux]$ pahole -C perf_session_env --reorganize --show_reorg_steps ~/bin/perf | tail -4
	/* --- cacheline 2 boundary (128 bytes) --- */

	/* size: 128, cachelines: 2, members: 20 */
};   /* saved 24 bytes and 1 cacheline! */
[acme@ssdandy linux]$

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-3d9tshamloinzxcqeb7mtd1n@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.h

@@ -77,16 +77,16 @@ struct perf_session_env {
 	unsigned long long	total_mem;
 
 	int			nr_cmdline;
-	char			*cmdline;
 	int			nr_sibling_cores;
-	char			*sibling_cores;
 	int			nr_sibling_threads;
-	char			*sibling_threads;
 	int			nr_numa_nodes;
-	char			*numa_nodes;
 	int			nr_pmu_mappings;
-	char			*pmu_mappings;
 	int			nr_groups;
+	char			*cmdline;
+	char			*sibling_cores;
+	char			*sibling_threads;
+	char			*numa_nodes;
+	char			*pmu_mappings;
 };
 
 struct perf_header {