Add tests for architecture filtering

Note that there is something surprising here: `EXCLUDE_ARCHS` _filters_
the architectures (i.e. runs it as %arch%), while `ARCH_FILTER` matches
exactly. This is exactly backwards from what the names suggest.

However, I am leaving this as is for the time being since there are
possibly existing wrappers that use these two variables in this way; a
further investigation should be done to ensure that we can improve this
in some sense. If we make such a change, we should regard it as breaking.

tests/test_build.py

+import os
 import re
 from pathlib import Path
 
+import pytest
+
 from .utils import run_ioc_get_output
 
 MODULE_VERSION = "0.0.0+0"
@@ -467,3 +470,28 @@ def test_updated_template_files(wrapper):
     rc, *_ = wrapper.run_make("db_internal")
     assert rc == 0
     assert db_file.read_text() == "record(ai, updated) {}"
+
+
+@pytest.mark.parametrize(
+    "installed_archs, param, expected",
+    [
+        ("foo bar baz foo-bar", "ARCH_FILTER=foo", ["foo"]),
+        ("foo", "EXCLUDE_ARCHS=foo", []),
+        ("foo-bar foo-baz baz baz-qux", "EXCLUDE_ARCHS=foo", ["baz", "baz-qux"]),
+    ],
+)
+def test_arch_filter(wrapper, installed_archs, param, expected):
+    arch_regex = re.compile(r"Pass 3: T_A =\s*([^\s]+)")
+
+    wrapper.add_var_to_makefile(
+        "CROSS_COMPILER_TARGET_ARCHS", installed_archs, modifier=""
+    )
+
+    rc, o, _ = wrapper.run_make("debug", param)
+
+    assert rc == 0
+
+    host_arch = os.getenv("EPICS_HOST_ARCH")
+    build_archs = [arch for arch in arch_regex.findall(o) if arch != host_arch]
+
+    assert build_archs == expected