Add $SYSTEMD_HWDB_UPDATE_BYPASS (#30463)

Same as $KERNEL_INSTALL_BYPASS, but for hwdb. This will speed up
cross architecture image builds in mkosi as I can disable package
managers from running the costly hwdb update stuff in qemu user
mode and run it myself with a native systemd-hwdb with --root=.

src/shared/hwdb-util.c

@@ -6,6 +6,7 @@
 
 #include "alloc-util.h"
 #include "conf-files.h"
+#include "env-util.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "fs-util.h"
@@ -710,3 +711,16 @@ bool hwdb_should_reload(sd_hwdb *hwdb) {
                 return true;
         return false;
 }
+
+int hwdb_bypass(void) {
+        int r;
+
+        r = getenv_bool("SYSTEMD_HWDB_UPDATE_BYPASS");
+        if (r < 0 && r != -ENXIO)
+                log_debug_errno(r, "Failed to parse $SYSTEMD_HWDB_UPDATE_BYPASS, assuming no.");
+        if (r <= 0)
+                return false;
+
+        log_debug("$SYSTEMD_HWDB_UPDATE_BYPASS is enabled, skipping execution.");
+        return true;
+}

src/shared/hwdb-util.h

@@ -8,3 +8,4 @@
 bool hwdb_should_reload(sd_hwdb *hwdb);
 int hwdb_update(const char *root, const char *hwdb_bin_dir, bool strict, bool compat);
 int hwdb_query(const char *modalias, const char *root);
+int hwdb_bypass(void);