linux-user: Use correct types in load_symbols()

Coverity doesn't like the code in load_symbols() which assumes
it can use 'int' for a variable that might hold an offset into
the guest ELF file, because in a 64-bit guest that could
overflow. Guest binaries with 2GB sections aren't very likely
and this isn't a security issue because we fully trust the
guest linux-user binary anyway, but we might as well use the
right types, which will placate Coverity. Use uint64_t to
hold section sizes, and bail out if the symbol table is too
large rather than just overflowing an int.

(Coverity issue CID1005776)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <1486249533-5260-1-git-send-email-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
