Declare some chars signed after the ARMv7hf compiler barfed
    like this:
    
    -mfpu=vfpv3-d16  -mfloat-abi=hard -c -o fmc.lo fmc.cpp
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
       {-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,0,1,2,3,4,5,6,7,8,-1,-1,-1,-1,-1,-1,-1};
                                                                                              ^
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    s3m.cpp:29:90: error: narrowing conversion of '-1' from 'int' to 'char' inside { } [-Wnarrowing]
    
    I wonder if it helps.