-fsigned-char breaks binary compatibility on ARM about android-cmake

[stefand]

char.txt

This test program shows the issue. Compile it with -fsigned-char and -funsigned-char (or no option at all) and compare the output. The exact symptom of the wrong setting depends on various factors like the selected C++ runtime library implementation and program behavior. My test program happens to work with gnustl with both char versions, but apitrace writes a bad stream. My test program doesn't write the 255 char with -fsigned-char with the default C++ library (libstdc++ I think).