fix MSVC OpenGL linkage warnings & mingw linker problems. use SDL.lib also for MinGW.

ExternalLibs/SDL12/lib/win32/libSDL.la

@@ -1,41 +0,0 @@
-# libSDL.la - a libtool library file
-# Generated by ltmain.sh (GNU libtool) 2.2.6
-#
-# Please DO NOT delete this file!
-# It is necessary for linking the library.
-
-# The name that we can dlopen(3).
-dlname='../bin/SDL.dll'
-
-# Names of this library.
-library_names='libSDL.dll.a'
-
-# The name of the static archive.
-old_library='libSDL.a'
-
-# Linker flags that can not go in dependency_libs.
-inherited_linker_flags=''
-
-# Libraries that this one depends upon.
-dependency_libs=' -luser32 -lgdi32 -lwinmm -ldxguid'
-
-# Names of additional weak libraries provided by this library
-weak_library_names=''
-
-# Version information for libSDL.
-current=11
-age=11
-revision=3
-
-# Is this an already installed library?
-installed=yes
-
-# Should we warn about portability when linking against -modules?
-shouldnotlink=no
-
-# Files to dlopen/dlpreopen
-dlopen=''
-dlpreopen=''
-
-# Directory that this library needs to be installed in:
-libdir='/usr/local/lib'