Add ubsan to the asan CI check.

We already have address sanitizer, so add "undefined" into the mix.

.cirrus.yml

@@ -73,9 +73,10 @@ gcc_task:
        USE_CONFIG: no
     - environment:
        USE_CONFIG: yes
-       CFLAGS: -std=c99 -pedantic -Wformat=2 -fsanitize=address
-       LDFLAGS: -fsanitize=address
+       CFLAGS: -std=c99 -pedantic -fsanitize=address,undefined -DHTS_ALLOW_UNALIGNED=0
+       LDFLAGS: -fsanitize=address,undefined
        USE_LIBDEFLATE: yes
+       UBSAN_OPTIONS: print_stacktrace=1:halt_on_error=1
 
   install_script: |
     apt-get update
@@ -109,7 +110,7 @@ ubuntu_task:
        DO_UNTRACKED_FILE_CHECK: yes
     - environment:
        USE_CONFIG: yes
-       CFLAGS: -g -Wall -O3
+       CFLAGS: -std=c99 -pedantic -Wformat=2 -g -Wall -O3
        USE_LIBDEFLATE: yes
 
   # NB: we could consider building a docker image with these