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

Run Build Command:"/usr/bin/make" "cmTC_ee0a6/fast"
make[1]: Entering directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_ee0a6.dir/build.make CMakeFiles/cmTC_ee0a6.dir/build
make[2]: Entering directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_ee0a6.dir/CheckSymbolExists.c.o
/home/buildroot/build/instance-0/output/host/bin/xtensa-buildroot-linux-uclibc-gcc --sysroot=/home/buildroot/build/instance-0/output/host/xtensa-buildroot-linux-uclibc/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mlongcalls -mauto-litpools -Os -g2    -o CMakeFiles/cmTC_ee0a6.dir/CheckSymbolExists.c.o   -c /home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_ee0a6
/home/buildroot/build/instance-0/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_ee0a6.dir/link.txt --verbose=1
/home/buildroot/build/instance-0/output/host/bin/xtensa-buildroot-linux-uclibc-gcc --sysroot=/home/buildroot/build/instance-0/output/host/xtensa-buildroot-linux-uclibc/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mlongcalls -mauto-litpools -Os -g2     -rdynamic CMakeFiles/cmTC_ee0a6.dir/CheckSymbolExists.c.o  -o cmTC_ee0a6 
CMakeFiles/cmTC_ee0a6.dir/CheckSymbolExists.c.o:(.text.startup+0x0): undefined reference to `PHYSFS_getPrefDir'
collect2: error: ld returned 1 exit status
CMakeFiles/cmTC_ee0a6.dir/build.make:97: recipe for target 'cmTC_ee0a6' failed
make[2]: *** [cmTC_ee0a6] Error 1
make[2]: Leaving directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_ee0a6/fast' failed
make[1]: *** [cmTC_ee0a6/fast] Error 2
make[1]: Leaving directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'

File /home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include </home/buildroot/build/instance-0/output/host/xtensa-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/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_38022/fast"
make[1]: Entering directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_38022.dir/build.make CMakeFiles/cmTC_38022.dir/build
make[2]: Entering directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_38022.dir/src.cxx.o
/home/buildroot/build/instance-0/output/host/bin/xtensa-buildroot-linux-uclibc-g++ --sysroot=/home/buildroot/build/instance-0/output/host/xtensa-buildroot-linux-uclibc/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -mlongcalls -mauto-litpools -Os -g2 -DHAVE_ICONV_CONST   -o CMakeFiles/cmTC_38022.dir/src.cxx.o -c /home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx
/home/buildroot/build/instance-0/output/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/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp/src.cxx:2:0:
/home/buildroot/build/instance-0/output/host/xtensa-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,
 ^~~~~
CMakeFiles/cmTC_38022.dir/build.make:65: recipe for target 'CMakeFiles/cmTC_38022.dir/src.cxx.o' failed
make[2]: *** [CMakeFiles/cmTC_38022.dir/src.cxx.o] Error 1
make[2]: Leaving directory '/home/buildroot/build/instance-0/output/build/supertux-0.6.0/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_38022/fast' failed
make[1]: *** [cmTC_38022/fast] Error 2
make[1]: Leaving directory '/home/buildroot/build/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; }