Make the build more fuzzer-friendly

This change adds support for the USE_ASAN=yes env variable, that builds
all minijail artifacts with -fsanitize=address. It also makes die() not
call abort(2) on failures, which confuses afl.

Bug: None
Test: minijail$ USE_ASAN=yes make clean all tests 2>/dev/null >/dev/null && \
               readelf -a syscall_filter_unittest | grep __asan_init
     000000313720  006200000001 R_X86_64_64       0000000000000000     __asan_init + 0
     00000031b9b0  006200000007 R_X86_64_JUMP_SLO 0000000000000000     __asan_init + 0
         98: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND        __asan_init
       1330: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND        __asan_init
     minijail$ USE_ASAN=no make clean all tests 2>/dev/null >/dev/null && \
               readelf -a syscall_filter_unittest | grep __asan_init
     minijail$
Test: USE_EXIT_ON_DIE=no make clean parse_seccomp_policy &&
      ./parse_seccomp_policy test/invalid_arg_filter.policy # aborts
Test: USE_EXIT_ON_DIE=yes make clean parse_seccomp_policy &&
      ./parse_seccomp_policy test/invalid_arg_filter.policy # exits
Change-Id: Ib9dcb271cd75335edd8b109149caf825f346322f
2 files changed