Determining if the PHYSFS_getPrefDir exist failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_1c1c5/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_1c1c5.dir/build.make CMakeFiles/cmTC_1c1c5.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_1c1c5.dir/CheckSymbolExists.c.o
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/mipsel-linux-gcc --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/mipsel-buildroot-linux-uclibc/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG   -o CMakeFiles/cmTC_1c1c5.dir/CheckSymbolExists.c.o   -c /home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_1c1c5
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_1c1c5.dir/link.txt --verbose=1
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/mipsel-linux-gcc --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/mipsel-buildroot-linux-uclibc/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG    CMakeFiles/cmTC_1c1c5.dir/CheckSymbolExists.c.o  -o cmTC_1c1c5 
/home/buildroot/autobuild/run/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/mipsel-buildroot-linux-uclibc/7.4.0/../../../../mipsel-buildroot-linux-uclibc/bin/ld: CMakeFiles/cmTC_1c1c5.dir/CheckSymbolExists.c.o: in function `main':
CheckSymbolExists.c:(.text.startup+0xc): undefined reference to `PHYSFS_getPrefDir'
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_1c1c5] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_1c1c5/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'


File /home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include </home/buildroot/autobuild/run/instance-1/output-1/host/mipsel-buildroot-linux-uclibc/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/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_91cf4/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_91cf4.dir/build.make CMakeFiles/cmTC_91cf4.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_91cf4.dir/src.cxx.o
/home/buildroot/autobuild/run/instance-1/output-1/host/bin/mipsel-linux-g++ --sysroot=/home/buildroot/autobuild/run/instance-1/output-1/host/mipsel-buildroot-linux-uclibc/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DHAVE_ICONV_CONST  -DNDEBUG   -o CMakeFiles/cmTC_91cf4.dir/src.cxx.o -c /home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx
/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx:4:9: 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/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx:2:0:
/home/buildroot/autobuild/run/instance-1/output-1/host/mipsel-buildroot-linux-uclibc/sysroot/usr/include/iconv.h:20:1: note: old declaration 'size_t iconv(iconv_t, char**, size_t*, char**, size_t*)'
 iconv(iconv_t cd, char **inbuf, size_t *inbytesleft,
 ^~~~~
make[2]: *** [CMakeFiles/cmTC_91cf4.dir/src.cxx.o] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_91cf4/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-1/output-1/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; }