testsuite: split out parts of jit.dg/jit.exp into a new lib/valgrind.exp

testsuite: split out parts of jit.dg/jit.exp into a new lib/valgrind.exp

I want to reuse some of the support for valgrind in jit.exp
in my upcoming testsuite for https://gcc.gnu.org/wiki/libdiagnostics
so this patch splits that out into a valgrind.exp.

No functional change intended.

gcc/testsuite/ChangeLog:
	* jit.dg/jit.exp: Add load_lib valgrind.exp.
	(proc report_leak): Move to valgrind.exp, and add argument
	leak_report_function rather than hardcoding xfail.
	(parse_valgrind_logfile): Likewise.
	(fixed_host_execute): Pass xfail to parse_valgrind_logfile.
	* lib/valgrind.exp: New file, based on the above.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>