Gdb pretty printers (#8263)

tests/untestable/gdb/gdb_pretty_printer_test_run.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# Exit if anything fails
+set -e
+#!/usr/bin/env bash
+# Compile the test project with fresh debug information.
+nim c --debugger:native gdb_pretty_printer_test_program.nim &> /dev/null
+# 2>&1 redirects stderr to stdout (all output in stdout)
+# <(...) is a bash feature that makes the output of a command into a
+# file handle.
+# diff compares the two files, the expected output, and the file
+# handle that is created by the execution of gdb.
+diff ./gdb_pretty_printer_test_output.txt <(gdb -x gdb_pretty_printer_test.py --batch-silent --args gdb_pretty_printer_test_program 2>&1)
+# The exit code of diff is forwarded as the exit code of this
+# script. So when the comparison fails, the exit code of this script
+# won't be 0. So this script should be embeddable in a test suite.