Treat bt_test.py failures as "SKIP" on freebsd.

Closes #18204.

changes/bug18204_028

@@ -0,0 +1,3 @@
+  o Testing:
+    - Treat backtrace test failures as expected on FreeBSD until we
+      solve bug 17808. Closes ticket 18204.

src/test/bt_test.py

@@ -39,7 +39,15 @@ for I in range(len(LINES)):
         print("OK")
         sys.exit(0)
 
+print("BAD")
+
 for l in LINES:
     print("{}".format(l), end="")
 
+if sys.platform.startswith('freebsd'):
+    # See bug #17808 if you know how to fix this.
+    print("Test failed; but FreeBSD is known to have backtrace problems.\n"
+          "Treating as 'SKIP'.")
+    sys.exit(77)
+
 sys.exit(1)

src/test/test_bt.sh

@@ -3,8 +3,8 @@
 
 exitcode=0
 
-"${builddir:-.}/src/test/test-bt-cl" backtraces || exit 77
-"${builddir:-.}/src/test/test-bt-cl" assert | "${PYTHON:-python}" "${abs_top_srcdir:-.}/src/test/bt_test.py" || exitcode=1
-"${builddir:-.}/src/test/test-bt-cl" crash  | "${PYTHON:-python}" "${abs_top_srcdir:-.}/src/test/bt_test.py" || exitcode=1
+"${builddir:-.}/src/test/test-bt-cl" backtraces || exit $?
+"${builddir:-.}/src/test/test-bt-cl" assert | "${PYTHON:-python}" "${abs_top_srcdir:-.}/src/test/bt_test.py" || exitcode="$?"
+"${builddir:-.}/src/test/test-bt-cl" crash  | "${PYTHON:-python}" "${abs_top_srcdir:-.}/src/test/bt_test.py" || exitcode="$?"
 
 exit ${exitcode}