perf tools: Provide subcmd configuration at runtime

Create init functions for exec_cmd.c and pager.c.  This allows their
configuration to be specified at runtime so they can be split out into a
separate library which can be used by other programs.  Their
configuration is stored in a shared subcmd_config struct.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/21f5f6b38da72c985a8dcfa185700d03e7eecd1d.1450193761.git.jpoimboe@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/perf.c b/tools/perf/perf.c
index 59ea48c..783a331 100644
--- a/tools/perf/perf.c
+++ b/tools/perf/perf.c
@@ -119,7 +119,7 @@
 {
 	switch (use_pager) {
 	case 0:
-		setenv("PERF_PAGER", "cat", 1);
+		setenv(PERF_PAGER_ENVIRONMENT, "cat", 1);
 		break;
 	case 1:
 		/* setup_pager(); */
@@ -530,6 +530,10 @@
 	const char *cmd;
 	char sbuf[STRERR_BUFSIZE];
 
+	/* libsubcmd init */
+	exec_cmd_init("perf", PREFIX, PERF_EXEC_PATH, EXEC_PATH_ENVIRONMENT);
+	pager_init(PERF_PAGER_ENVIRONMENT);
+
 	/* The page_size is placed in util object. */
 	page_size = sysconf(_SC_PAGE_SIZE);
 	cacheline_size = sysconf(_SC_LEVEL1_DCACHE_LINESIZE);