A note for my future self on how to compile a library as universal binary in Mac OS X.

For a while, I’ve been getting warnings like these when building pymssql:

ld: warning: ignoring file /usr/local/lib/libsybdb.dylib, 
file was built for unsupported file format 
( 0xcf 0xfa 0xed 0xfe 0x 7 0x 0 0x 0 0x 1 0x 3 0x 0 0x 0 0x 0 0x 6 0x 0 0x 0 0x 0 ) 
which is not the architecture being linked (i386): 
/usr/local/lib/libsybdb.dylib
ld: warning: ignoring file /usr/local/lib/libct.dylib, 
file was built for unsupported file format 
( 0xcf 0xfa 0xed 0xfe 0x 7 0x 0 0x 0 0x 1 0x 3 0x 0 0x 0 0x 0 0x 6 0x 0 0x 0 0x 0 ) 
which is not the architecture being linked (i386): 
/usr/local/lib/libct.dylib

I finally decided to do something about them. I rebuilt FreeTDS from source as follows:

./configure \
    CFLAGS="-arch i386 -arch x86_64" \
    CXXFLAGS="-arch i386 -arch x86_64" \
    LDFLAGS="-arch i386 -arch x86_64" \
    --disable-dependency-tracking
make
make install

Goodbye warnings!

This Stack Overflow post was helpful: Stack Overflow: How to compile universal libraries on Mac OS X?