Fixed PR10395 by making the kmodule.exp testcase use a custom module.

* testsuite/systemtap.base/kmodule.exp: Instead of depending on the 'ext3'
  module (which is no longer a module on newer kernels), build and install
  our own test module, run the test, then remove the module.
* testsuite/systemtap.base/kprobe_module.stp: Changed to probe the new
  test module.
* testsuite/systemtap.base/stap_kmodule.Makefile: New file.
* testsuite/systemtap.base/stap_kmodule.c: Ditto.
Update PR15673 fix in loc2c-runtime.h.

* runtime/loc2c-runtime.h: If STP_SKIP_BADVARS is defined, don't have two
  different CATCH_DEREF_FAULT definitions.
Fix PR15675 by making 'probe kprobe.module("foo").function("bar") work.

* tapsets.cxx (kprobe_derived_probe_group::emit_module_decls): Fix emitted
  kprobe_resolve() to lookup "module:function" symbols correctly.
miscellany: support '\x' hex codes in string literal
Add a new test for probing 'kprobe.module("foo").function("bar") (PR15675).

* testsuite/systemtap.base/kprobe_module.stp: Add new test for
  'kprobe.module("foo").function("bar")'.
* testsuite/systemtap.base/kmodule.exp: Run new kprobe_module.stp test.
parser: note PR13371 in eschewing \FOO processing during lexing.