Expect lib.libc.sys.getcontext_test.setcontext_link to fail on amd64; add

additional debugging to make the underlying problem more visible

Calling setcontext(2) on amd64 as shown in the test program is failing on
amd64, not i386, with a return code of -1 and an errno of EINVAL

Further investigation is being done in the PR to determine the root cause for
the failure

PR: 194828
Tested with the following configuration:
- amd64/i386
- 11.0-CURRENT @ r273153
- 100 times in a tight loop as root with the following commands...
-- kyua test lib/libc
-- kyua test lib/libc/sys
-- kyua test lib/libc/sys/getcontext_test

contrib/netbsd-tests/lib/libc/sys/t_getcontext.c

@@ -101,6 +101,13 @@ ATF_TC_BODY(setcontext_link, tc)
 	ucontext_t save;
 	volatile int i = 0; /* avoid longjmp clobbering */
 
+#ifdef __FreeBSD__
+#ifdef __amd64__
+	atf_tc_expect_fail("setcontext in this testcase fails on "
+	    "FreeBSD/amd64 with rc == -1/errno == EINVAL; see PR # 194828");
+#endif
+#endif
+
 	for (i = 0; i < DEPTH; ++i) {
 		ATF_REQUIRE_EQ(getcontext(&uc[i]), 0);
 
@@ -114,8 +121,15 @@ ATF_TC_BODY(setcontext_link, tc)
 
 	ATF_REQUIRE_EQ(getcontext(&save), 0);
 
+#ifdef __FreeBSD__
+	if (calls == 0) {
+		int rc = setcontext(&uc[DEPTH-1]);
+		ATF_REQUIRE_EQ_MSG(rc, 0, "%d != 0; (errno = %d)", rc, errno);
+	}
+#else
 	if (calls == 0)
 		ATF_REQUIRE_EQ(setcontext(&uc[DEPTH-1]), 0);
+#endif
 }
 
 ATF_TP_ADD_TCS(tp)