mtest: set MSAN_OPTIONS to abort by default

Followup to 7b7d2e0 which handles ASAN and UBSAN.

It turns out that MSAN needs the same treatment. I've checked other sanitizers
like HWASAN and TSAN - it looks like they may both need it too, but Meson doesn't
currently suppose those anyway (see mesonbuild#12648).

(TODO: Should we just set those anyway pre-emptively?)
(TODO: docs)

Signed-off-by: Sam James <sam@gentoo.org>

mesonbuild/mtest.py

@@ -1414,6 +1414,8 @@ def __init__(self, test: TestSerialisation, env: T.Dict[str, str], name: str,
             env['ASAN_OPTIONS'] = 'halt_on_error=1:abort_on_error=1:print_summary=1'
         if ('UBSAN_OPTIONS' not in env or not env['UBSAN_OPTIONS']):
             env['UBSAN_OPTIONS'] = 'halt_on_error=1:abort_on_error=1:print_summary=1:print_stacktrace=1'
+        if ('MSAN_OPTIONS' not in env or not env['MSAN_OPTIONS']):
+            env['UBSAN_OPTIONS'] = 'halt_on_error=1:abort_on_error=1:print_summary=1:print_stacktrace=1'
 
         if self.options.gdb or self.test.timeout is None or self.test.timeout <= 0:
             timeout = None