support: Introduce new subdirectory for test infrastructure

The new test driver in <support/test-driver.c> has feature parity with
the old one.  The main difference is that its hooking mechanism is
based on functions and function pointers instead of macros.  This
commit also implements a new environment variable, TEST_COREDUMPS,
which disables the code which disables coredumps (that is, it enables
them if the invocation environment has not disabled them).

<test-skeleton.c> defines wrapper functions so that it is possible to
use existing macros with the new-style hook functionality.

This commit changes only a few test cases to the new test driver, to
make sure that it works as expected.

malloc/tst-malloc-backtrace.c

@@ -16,9 +16,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-
+#include <signal.h>
 #include <stdlib.h>
 
+#include <support/support.h>
+
 #define SIZE 4096
 
 /* Wrap free with a function to prevent gcc from optimizing it out.  */
@@ -30,13 +32,6 @@ call_free (void *ptr)
   *(size_t *)(ptr - sizeof (size_t)) = 1;
 }
 
-int do_test (void);
-
-#define TEST_FUNCTION do_test ()
-#define EXPECTED_SIGNAL SIGABRT
-
-#include "../test-skeleton.c"
-
 int
 do_test (void)
 {
@@ -53,3 +48,6 @@ do_test (void)
      doesn't optimize out that malloc call.  */
   return (ptr1 == ptr2);
 }
+
+#define EXPECTED_SIGNAL SIGABRT
+#include <support/test-driver.c>