Make gdb script work on mac and linux; add windows gdb script (#13453)

bin/nim-gdb.bat

@@ -0,0 +1,16 @@
+@echo off
+for %%i in (nim.exe) do (set NIM_BIN=%%~dp$PATH:i)
+
+for %%i in ("%NIM_BIN%\..\") do (set NIM_ROOT=%%~fi)
+
+set @GDB_PYTHON_MODULE_PATH=%NIM_ROOT%\tools\nim-gdb.py
+set @NIM_GDB=gdb.exe
+
+@echo source %@GDB_PYTHON_MODULE_PATH%> wingdbcommand.txt
+
+%@NIM_GDB% --command="wingdbcommand.txt" %*
+
+del wingdbcommand.txt /f /q
+
+EXIT /B %ERRORLEVEL%
+@echo on