Determining if the PHYSFS_getPrefDir exist failed with the following output:
Change Dir: /home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_4674e/fast"
make[1]: Entering directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_4674e.dir/build.make CMakeFiles/cmTC_4674e.dir/build
make[2]: Entering directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_4674e.dir/CheckSymbolExists.c.o
/home/dawncrow/buildroot-test/scripts/instance-0/output/host/bin/mips-linux-gnu-gcc --sysroot=/home/dawncrow/buildroot-test/scripts/instance-0/output/host/mips-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG   -o CMakeFiles/cmTC_4674e.dir/CheckSymbolExists.c.o   -c /home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_4674e
/home/dawncrow/buildroot-test/scripts/instance-0/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_4674e.dir/link.txt --verbose=1
/home/dawncrow/buildroot-test/scripts/instance-0/output/host/bin/mips-linux-gnu-gcc --sysroot=/home/dawncrow/buildroot-test/scripts/instance-0/output/host/mips-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG    -rdynamic CMakeFiles/cmTC_4674e.dir/CheckSymbolExists.c.o  -o cmTC_4674e 
CMakeFiles/cmTC_4674e.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text.startup+0x0): undefined reference to `PHYSFS_getPrefDir'
CheckSymbolExists.c:(.text.startup+0x8): undefined reference to `PHYSFS_getPrefDir'
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_4674e] Error 1
make[2]: Leaving directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_4674e/fast] Error 2
make[1]: Leaving directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'

File /home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include </home/dawncrow/buildroot-test/scripts/instance-0/output/host/mips-buildroot-linux-gnu/sysroot/usr/include/physfs.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef PHYSFS_getPrefDir
  return ((int*)(&PHYSFS_getPrefDir))[argc];
#else
  (void)argc;
  return 0;
#endif
}

Performing C++ SOURCE FILE Test HAVE_ICONV_CONST failed with the following output:
Change Dir: /home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_0e2d0/fast"
make[1]: Entering directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_0e2d0.dir/build.make CMakeFiles/cmTC_0e2d0.dir/build
make[2]: Entering directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_0e2d0.dir/src.cxx.o
/home/dawncrow/buildroot-test/scripts/instance-0/output/host/bin/mips-linux-gnu-g++ --sysroot=/home/dawncrow/buildroot-test/scripts/instance-0/output/host/mips-buildroot-linux-gnu/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DHAVE_ICONV_CONST  -DNDEBUG   -o CMakeFiles/cmTC_0e2d0.dir/src.cxx.o -c /home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx
/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx:4:98: error: ambiguating new declaration of 'double iconv(iconv_t, char**, size_t*, char**, size_t*)'
  double iconv(iconv_t cd,  char **inbuf, size_t *inbytesleft, char **outbuf, size_t *outbytesleft);
                                                                                                  ^
In file included from /home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx:2:0:
/home/dawncrow/buildroot-test/scripts/instance-0/output/host/mips-buildroot-linux-gnu/sysroot/usr/include/iconv.h:42:15: note: old declaration 'size_t iconv(iconv_t, char**, size_t*, char**, size_t*)'
 extern size_t iconv (iconv_t __cd, char **__restrict __inbuf,
               ^
make[2]: *** [CMakeFiles/cmTC_0e2d0.dir/src.cxx.o] Error 1
make[2]: Leaving directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_0e2d0/fast] Error 2
make[1]: Leaving directory `/home/dawncrow/buildroot-test/scripts/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'

Source file was:

	#include <iconv.h>
	// this declaration will fail when there already exists a non const char** version which returns size_t
	double iconv(iconv_t cd,  char **inbuf, size_t *inbytesleft, char **outbuf, size_t *outbytesleft);
	int main() { return 0; }