travis: add AddressSanitizer build rules

The AddressSanitizer sanitizer will be used only when compiling with
clang and performing testing as root, so that the sanitizer has maximal
coverage.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
blkdiscard: include missing header

Commit 700031ade7cbcdcecf1205f98f50ed0da57c7493 missed an include.

sys-utils/blkdiscard.c:182:2: warning: implicit declaration of function
'gettime_monotonic' is invalid in C99 [-Wimplicit-function-declaration]

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
lib/mbalign: fix unsigned integer overflow [AddressSanitizer]

This error was reported 155 times.

lib/mbsalign.c:322:18: runtime error: unsigned integer overflow: 0 - 1
cannot be represented in type 'size_t' (aka 'unsigned long')

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
cal: fix signed integer overflow [AddressSanitizer]

misc-utils/cal.c:811:16: runtime error: signed integer overflow:
2147483645 + 536870911 cannot be represented in type 'int'

Signed-off-by: Sami Kerola <kerolasa@iki.fi>