perf pmu: Include the headers that are used

pmu.c uses errno, free() and the str*() functions but declares none of
them directly. <string.h> arrives by way of <linux/string.h>, and
<errno.h> and <stdlib.h> come from whatever the other headers happen to
drag in, which is fragile and breaks on C libraries that don't nest
their headers the same way.

Include the three directly.

<ctype.h> is deliberately not added. The isdigit(), tolower() and
toupper() used here are the macros from <linux/ctype.h>, which is
included on purpose and documents that it doesn't handle EOF the way the
standard C library does, so pulling in <ctype.h> would change which
implementation is used.

size_t is left alone too, as <stdio.h> is already included directly and
declares it.

No functional change.

Signed-off-by: Ian Rogers <irogers@google.com>
Assisted-by: Antigravity:gemini-3.1-pro
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/pmu.c

@@ -8,8 +8,11 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
-#include <stdio.h>
+#include <errno.h>
 #include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <dirent.h>
 #include <api/fs/fs.h>
 #include <api/io.h>