cmake 3.9 for android is broken
-isystem /usr/include is appended to compiler flags. clang will not prefix
SYSROOT for those dirs, instead
-iwithsysroot /usr/include should be used. gcc is a little different. According the document https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html
Add the directory dir to the list of directories to be searched for header files during preprocessing. If dir begins with ‘=’ or $SYSROOT, then the ‘=’ or $SYSROOT is replaced by the sysroot prefix; see --sysroot and -isysroot.
-isystem =/usr/include should be used.