Fix log_backtrace assertion failure caused by LP64 fix.
When libc.debug.malloc is enabled, stack backtraces fail with:
bionic/libc/bionic/libc_logging.cpp:378: assertion "conversion
specifier unsupported" failed
The cause was a change to the format specifier from "%08x" to
"%0*x" to pass the field width as an additional parameter.
Unfortunately this modifier isn't supported by out_vformat() in
libc_logging.cpp.
Changed to use "%016x" if __LP64__ is defined; "%08x" otherwise.
Bug:
13177507
Change-Id: Ibf07263acf14da086d3c3788872f4b5477bd5708