Extend and document compiler debugging utilities (#19841)

* Add two debugutils procs that native debuggers can break on use to
  execute commands when code of interest is being compiled.
* Add GDB and LLDB programs to disable and enable breakpoints and
  watchpoints when code of interest is being compiled.
* Extend the `intern.rst` docs regarding debugging the compiler.

Co-authored-by: quantimnot <quantimnot@users.noreply.github.com>

tools/compiler.gdb

@@ -0,0 +1,39 @@
+# create a breakpoint on `debugutils.enteringDebugSection`
+define enable_enteringDebugSection
+	break -function enteringDebugSection
+	# run these commands once breakpoint enteringDebugSection is hit
+	command
+		# enable all breakpoints and watchpoints
+		enable
+		# continue execution
+		cont
+	end
+end
+
+# create a breakpoint on `debugutils.exitingDebugSection` named exitingDebugSection
+define enable_exitingDebugSection
+	break -function exitingDebugSection
+	# run these commands once breakpoint exitingDebugSection is hit
+	command
+		# disable all breakpoints and watchpoints
+		disable
+		# but enable the enteringDebugSection breakpoint
+		enable_enteringDebugSection
+		# continue execution
+		cont
+	end
+end
+
+# some commands can't be set until the process is running, so set an entry breakpoint
+break -function NimMain
+# run these commands once breakpoint NimMain is hit
+command
+	# disable all breakpoints and watchpoints
+	disable
+	# but enable the enteringDebugSection breakpoint
+	enable_enteringDebugSection
+	# no longer need this breakpoint
+	delete -function NimMain
+	# continue execution
+	cont
+end