[PATCH] Makefile: suppress annotated leaks with certain ASan options

When building with `SANITIZE=leak`, we define `SUPPRESS_ANNOTATED_LEAKS` in order to make the `UNLEAK()` macro work (without the aforementioned define, `UNLEAK()` is a noop). This is from `UNLEAK()`'s introduction in 0e5bba53af (add UNLEAK annotation for reducing leak false positives, 2017-09-08), where `UNLEAK()` is a noop for performance reasons unless we are using the leak sanitizer.

However, it is possible to use the leak sanitizer without `SANITIZE=leak`. This happens when building with `SANITIZE=address` and enabling the leak sanitizer via the `ASAN_OPTIONS` variable (by including the string "detect_leaks=1").

This renders `UNLEAK()` useless when doing `SANITIZE=address` builds which also use the leak checker.

Update our Makefile to pretend as if `SANITIZE=leak` was given when `SANITIZE=address` is given and the leak checker is enabled via `ASAN_OPTIONS`.

Playing around with all five options (two spelling "enabled", two spelling "disabled", and the empty set of options) yields the correct behavior:

    for opt in '' detect_leaks=1 detect_leaks=true detect_leaks=0 detect_leaks=false
    do
      echo "==> ${opt:-(nothing)}"
      make -B builtin/add.o V=1 SANITIZE=address ASAN_OPTIONS="$opt" 2>&1 |
        grep -o -- '-DSUPPRESS_ANNOTATED_LEAKS'
    done

gives us:

    ==> (nothing)
    -DSUPPRESS_ANNOTATED_LEAKS
    ==> detect_leaks=1
    -DSUPPRESS_ANNOTATED_LEAKS
    ==> detect_leaks=true
    -DSUPPRESS_ANNOTATED_LEAKS
    ==> detect_leaks=0
    ==> detect_leaks=false

Making it possible to rely on `UNLEAK()` when implicitly using the leak checker via SANITIZE=address builds.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
I found this while playing around with GitHub's ASan-enabled CI builds
for our internal fork following a merge with v2.38.3.

The check-chainlint recipe in t/Makefile started using "git diff" via d00113ec34 (t/Makefile: apply chainlint.pl to existing self-tests, 2022-09-01), which triggered a leak in some of GitHub's custom code. I was surprised when marking the variable with UNLEAK() didn't do the trick, and ended up down this rabbit hole ;-).

 Makefile | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)