libctf: suppress spurious failure of malloc-counting tests under valgrind

The libctf-regression/open-error-free.c test works by interposing malloc
and counting mallocs and frees across libctf operations.  This only
works under suitably-interposable mallocs on systems supporting
dlsym (RTLD_NEXT, ...), so its operation is restricted to glibc
systems for now, but also it interacts badly with valgrind, which
interposes malloc itself.  Detect a running valgrind and skip the test.

Add new facilities allowing libctf lookup tests to declare themselves
unsupported, by printing "UNSUPPORTED: " and then some meaningful
message instead of their normal output.

libctf/
	* configure.ac: Check for <valgrind/valgrind.h>.
	* config.h.in: Regenerate.
	* configure: Likewise.
	* testsuite/lib/ctf-lib.exp (run_lookup_test): Add support for
	UNSUPPORTED tests.
	* testsuite/libctf-regression/open-error-free.c: When running
	under valgrind, this test is unsupported.

libctf/testsuite/libctf-regression/open-error-free.c

@@ -1,6 +1,7 @@
 /* Make sure that, on error, an opened dict is properly freed.  */
 
 #define _GNU_SOURCE 1
+#include "config.h"
 #include <dlfcn.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -8,6 +9,10 @@
 #include <ctf-api.h>
 #include <ctf.h>
 
+#ifdef HAVE_VALGRIND_VALGRIND_H
+#include <valgrind/valgrind.h>
+#endif
+
 static unsigned long long malloc_count;
 static unsigned long long free_count;
 
@@ -111,6 +116,14 @@ int main (void)
   ctf_next_t *it = NULL;
   unsigned long long frozen_malloc_count, frozen_free_count;
 
+#ifdef HAVE_VALGRIND_VALGRIND_H
+  if (RUNNING_ON_VALGRIND)
+    {
+      printf ("UNSUPPORTED: valgrind interferes with malloc counting\n");
+      return 0;
+    }
+#endif
+
   if ((fp = ctf_create (&err)) == NULL)
     goto open_err;