elfcore.c: do not use sizeof with VLA
elfcore.c: do not use sizeof with VLA

Expression sizeof(scratch) doesn't work properly when using --std=c++1y in g++ 4.9.
It seems that in this mode g++ assumes it is a constant-time expression equal to sizeof(char)
instead of substituting the run-time value of the variable-length array size,
leading to the malformed core dump.

madscientist/google-coredumper,anatol/google-coredumper,AmadeusITGroup/CoreDumper,anatol/google-coredumper,madscientist/google-coredumper,anatol/google-coredumper,AmadeusITGroup/CoreDumper,AmadeusITGroup/CoreDumper,madscientist/google-coredumper