Windows build: alternative makefile

This is a separate makefile for MSVC builds. It is deliberately put in
another dir than src/ and lib/ to allow a different build experience
than the previous - at least during a period. Eventually we should
unify.

winbuild/gen_resp_file.bat

@@ -0,0 +1,6 @@
+@echo OFF
+@del %OUTFILE%
+@echo %MACRO_NAME% = \> %OUTFILE%
+@for %%i in (%*) do @echo		%LIBCURL_DIROBJ%/%%i \>>  %OUTFILE%
+@echo. >>  %OUTFILE%
+:END