JIT, testsuite, Darwin: Initial testsuite fixes.

JIT, testsuite, Darwin: Initial testsuite fixes.

The testsuite setup for jit is not compatible with Darwin since it
assumes that all targets support --export-dynamic.

 - this is fixed by adding '-rdynamic' conditionally upon target
   support for that (-rdynamic will be converted to the appropriate
   linker option).

There is also an assumption that a suitable version of dejagnu.h
is present in some default include search path that is usable from
the testsuite.  This is not the case for Darwin (dejagnu.h is not
installed, and would not, in general, be found in any default include
search path if installed via one of the main 'distros').  Also the
upstream dejagnu.h has a definition of 'wait()' that clashes with a
libc routines and therefore causes fails in the testsuite.

 - This patch imports the header from dejagnu-1.6.2 and
   * renames it to 'jit-dejagnu.h'
   * patches it to avoid unused variable warnings and the clash
     with the libc definition of wait ()
   * In accordance with the advice in the expect man page, ensures
     that the final output of the 'totals' print is stable.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
gcc/jit/ChangeLog:

	* docs/examples/tut04-toyvm/toyvm.c: Include jit-dejagnu.h.
	* docs/examples/tut04-toyvm/toyvm.cc: Likewise.
	* jit-dejagnu.h: New file, imported from dejagnu-1.6.2 and
	patched for this application.

gcc/testsuite/ChangeLog:

	* jit.dg/harness.h: Include jit-dejagnu.h.
	* jit.dg/jit.exp: Use -rdynamic conditionally on target
	support, instead of unconditional -Wl,--export-dynamic.

(cherry picked from commit eea1677fd03a1cb820cbb72044d4a0770f8a7a93)