Port most of libdispatch tests to Linux (31 compile; 21 pass).

Made an initial sweep through the test suite to resolve
the easy compilation issues.

Summary of changes:
 (a) Guard mach specific code with #ifdef __APPLE__
 (b) Changes to tests/Makefile.am to preserve
     information from configure to guide test selection,
     compilation, and execution.
 (c) Map sysctlbyname calls to sysconf
 (d) Simulate mach_absolute_time APIs
 (e) Guard code using F_NOCACHE and F_GLOBAL_NOCACHE
 (f) On Linux, simplify bsdtestharness.c to not use
     libdispatch to execute the test cases (some of the
     needed libdispatch functionality is not yet working).

To track progress, we broke the TESTS list in tests/Makefile.am
into UNPORTED_TESTS, PORTED_TESTS_FAILED, PORTED_TESTS_PASSED.
TESTS is defined as the union of PORTED_TESTS_PASSED and
PORTED_TESTS_FAILED.
If the automake testing harness is only being used on Linux,
it would be nice to merge this change back to coordinate progress.
If you use this test harnesss on OS X too, we can do something
different like tracking progress in a side file instead.

Signed-off-by: Daniel A. Steffen <dsteffen@apple.com>

configure.ac

@@ -115,8 +115,11 @@ AS_IF([test "x$DTRACE" != "x"], [use_dtrace=true],[
 AM_CONDITIONAL(USE_DTRACE, $use_dtrace)
 AC_PATH_PROG(LEAKS, leaks)
 AS_IF([test "x$LEAKS" != "x"],
-  [AC_DEFINE(HAVE_LEAKS, 1, [Define if Apple leaks program is present])]
+  [AC_DEFINE(HAVE_LEAKS, 1, [Define if Apple leaks program is present])
+   have_leaks=true],
+  [have_leaks=false]
 )
+AM_CONDITIONAL(HAVE_LEAKS, $have_leaks)
 
 DISPATCH_C_ATOMIC_BUILTINS