x86, kaslr: Use char array to gain sizeof sanity

The build_str needs to be char [] not char * for the sizeof() to report
the string length.

Reported-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/20131112165607.GA5921@www.outflux.net


Signed-off-by: H. Peter Anvin <hpa@zytor.com>