方法很简单，比如：
C:CodeBlocksMinGWlibdx9>reimp d3d8.lib
就会生成一个“libd3d8.a”文件，这个文件就可以让基于MinGW的编译器链接使用了。
我用这个方法成功的把DirectX9c的.lib库转化成了.a库，并在CodeBlocks下编译成功了其生成的dx项目，
但是有三个.lib文件无法通过这个方法转换：DxErr.lib、DxErr8.lib、DxErr9.lib，估计其他方法，
但似乎没有他们也不影响DX9c库的使用，先这样，需要的话再想办法吧。
还有一个办法，来源是：
http://topic.csdn.net/t/20040721/11/3195357.htm
不知道是否可行，可以试试。
GCC和VC都使用COFF格式，所以VC中的.obj .lib与gcc用的.o .a是一样的（在WINDOWS下），只是扩展名不一样，通常你只要改一下名称就OK啦！不过有些库不行，因为库中的代码可能会用到一些编译器专有的特性，用VC做的.lib可能在gcc下没法通过编译（缺少符号），反之亦然。
reimp的readme文档内容如下：
README for reimp
================
* Overview
`reimp' is a tool to convert Microsoft's new-style (short) import
libraries to import libraries for win32 ports of GNU tools (mingw32,
cygwin).
`reimp' reads an MS import library and writes all imports to the
corresponding .DEF file(s) that it feeds to `dlltool' that creates the
import library.
* Invocation
Usage: reimp [options] IMPLIB
Options:
-s, --dump-symbols dump symbols to stdout
-d, --only-def only create .def files
-c, --keep-case keep case in lib*.a file names
--dlltool use for dlltool
--as use for assembler
The `--dump-symbols' option makes `reimp' use a quick method for
finding imported symbols and sending the names of found symbols to
stdout. If the input library contain non-imported symbols they will be
listed as well. The output symbols will have all decoration preserved
(i.e '_' will prefix most symbols), so if you feed it to dlltool you
should strip leading underscores. For example
echo EXPORTS > imp.def
reimp imp.lib | sed 's/_//' >> imp.def
dlltool -k --def imp.def --output-lib libimp.a --dllname imp.dll
The `--only-def' option makes `reimp' stop after generating the .DEF
file(s).
By default `reimp' converts all output library names to lower-case. By
using the `keep-case' option `reimp' will use exactly the case of the
DLL imported from when creating an import library. KERNEL32.dll will
generate libKERNEL32.a and not libkernel32.a as it would be default.
* Notes on mixed libraries
If an input library contain regular objects (non-imports, i.e code and
data) `reimp' will write out those objects unless you specify one of
the `--only-def' and `--dump-symbols' options. You probably want to
include those objects as well in the generated library. `reimp'
doesn't do that automatically so you have to do it manually using
`ar', like this
reimp imp.lib # this generates several .o or .obj files.
ar rcs libimp.a *.obj # add them to library
* Contact information
如果没有reimp
下载mingw-utils
http://sourceforge.net/projects/mingw/files/MinGW/Utilities/mingw-utils/mingw-utils-0.3/mingw-utils-0.3.tar.gz/download
下载mingw-utils-0.3.tar.gz，解压，将其中的reimp copy至MinGW的bin目录下。
使用reimp和dlltool
进入cmd下
cd c:\mysql\lib\opt
reimp -d libmysql.lib
dlltool -k -d libmysql.def -l libmysql.a
