Why is libtool looking for .lib files instead of .a files?

Question

I am in the process of cross-compiling Fontconfig for Windows using Mingw-w64 (the host is Ubuntu 12.04 64-bit). The process consists of the following steps:

1. Compile and install the build dependencies (Freetype and eXpat).

2. Run ./configure:

   ./configure --host=i686-win64-mingw32 --prefix=/usr/i686-w64-mingw32
   

3. The ./configure process completes without error and I run make:

   make
   

4. Unfortunately something goes wrong here:

   ...
     CCLD   libfontconfig.la
   i686-w64-mingw32-gcc: error: /usr/i686-w64-mingw32/lib/libexpat.lib:
       No such file or directory
   

As you can see, libtool is looking for libexpat.lib for some strange reason (which doesn't exist) instead of libexpat.a (which does exist).

What's going on here?

---

Edit: to make things more confusing, these same steps work perfectly on Ubuntu 12.10 (Quantal). I have no clue why it's failing on 12.04 (Precise). A diff of the output from the commands above yields no difference until the line containing the error above.

---

Further edit: I've extracted the raw command being run that generates the error:

/bin/bash ../libtool --silent --tag=CC --mode=link i686-w64-mingw32-gcc -O2 -ve
rsion-info 7:2:6 -no-undefined -export-symbols fontconfig.def -o libfontconfig.l
a -rpath /usr/i686-w64-mingw32/lib fcatomic.lo fcblanks.lo fccache.lo fccfg.lo 
fccharset.lo fcdbg.lo fcdefault.lo fcdir.lo fcformat.lo fcfreetype.lo fcfs.lo fc
init.lo fclang.lo fclist.lo fcmatch.lo fcmatrix.lo fcname.lo fcpat.lo fcserializ
e.lo fcstat.lo fcstr.lo fcxml.lo ftglue.lo -L/usr/i686-w64-mingw32/lib -lfreetyp
e -L/usr/i686-w64-mingw32/lib -lexpat

The call to i686-w64-mingw32-gcc becomes:

--------------------------------------------------------------------------------
i686-w64-mingw32-gcc -shared .libs/libfontconfig-1.dll.def .libs/fcatomic.o .lib
s/fcblanks.o .libs/fccache.o .libs/fccfg.o .libs/fccharset.o .libs/fcdbg.o .libs
/fcdefault.o .libs/fcdir.o .libs/fcformat.o .libs/fcfreetype.o .libs/fcfs.o .lib
s/fcinit.o .libs/fclang.o .libs/fclist.o .libs/fcmatch.o .libs/fcmatrix.o .libs/
fcname.o .libs/fcpat.o .libs/fcserialize.o .libs/fcstat.o .libs/fcstr.o .libs/fc
xml.o .libs/ftglue.o -L/usr/i686-w64-mingw32/lib /usr/i686-w64-mingw32/lib/libfr
eetype.dll.a /usr/i686-w64-mingw32/lib/libexpat.lib -O2 -o .libs/libfontconfig-1
.dll -Wl,--enable-auto-image-base -Xlinker --out-implib -Xlinker .libs/libfontco
nfig.dll.a

Answer 1

So it turns out the problem wasn't with Fontconfig at all but with eXpat. The environment used to build eXpat didn't have Mingw-w64's C++ compiler installed and for some reason that resulted in a file named libexpat.a instead of libexpat.dll.a.

Once I retried the build with the g++-mingw-w64 package installed, it succeeded.

Incidentally, the reason that the Quantal build succeeded while the Precise build failed is due to the fact that g++-mingw-w64 is not a dependency of mingw-w64 on Precise but has become a dependency on Quantal.