As a follow-up to my own post, I want to tell those reading that I have looked in the .a file and the symbol is present:

simsong@FC15:~/domex/src/bulk_extractor/src$ x86_64-w64-mingw32-nm /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libexiv2.a |grep Exiv25Value8toStringEv                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
00000000000067b0 T _ZNK5Exiv25Value8toStringEv
                 U _ZNK5Exiv25Value8toStringEv
simsong@FC15:~/domex/src/bulk_extractor/src$

I find this very confusing and welcome any help.