cross platform c++ source has link error

I have a cross-platform application and I want to compile it on Mac OS X 10.4.11
There are some functions for using load, and free external library and get its functions and they are defined for each platform by #if defined(_WIN32) || defined(_WIN64) and #elif defined(__Apple__).

But there is errors like
NEXT_ROOT environment variable ignored because -syslibroot specified
Undefined symbols:
_LibraryFree
_LibraryGetFunc
_LibraryOpen
.............../.../.../ppc/someIM.o reference to undefined _LibraryFree
... same as above for _LibraryGetFunc
... same as above for _LibraryOpen
internal link edit command failed

I specified MacOSX10.3.9.sdk for SDKROOT_ppc and MacOSX10.4u.sdk for SDKROOT_i386.

Is there anyone guess what the problem is ?