meson: Simplify asan-options handling even more

Instead of specifying env variables all the time
we can instead embed the __asan_default_options symbol
in all executables / shared objects. This reduces code
duplication.

src/libfetchers-tests/meson.build

@@ -63,7 +63,7 @@ this_exe = executable(
 test(
   meson.project_name(),
   this_exe,
-  env : asan_test_options_env + {
+  env : {
     '_NIX_TEST_UNIT_DATA' : meson.current_source_dir() / 'data',
   },
   protocol : 'gtest',

src/libfetchers-tests/package.nix

@@ -61,7 +61,6 @@ mkMesonExecutable (finalAttrs: {
             buildInputs = [ writableTmpDirAsHomeHook ];
           }
           ''
-            export ASAN_OPTIONS=abort_on_error=1:print_summary=1:detect_leaks=0
             export _NIX_TEST_UNIT_DATA=${resolvePath ./data}
             ${stdenv.hostPlatform.emulator buildPackages} ${lib.getExe finalAttrs.finalPackage}
             touch $out