add possibility to pass parameters to cmake when building debian package

PiperOrigin-RevId: 555935217

Author: eustas

debian/rules

@@ -1,6 +1,11 @@
 #!/usr/bin/make -f
+
+# This variable could be set via --set-envvar=HWY_EXTRA_CONFIG=
+# Safeguard: turn undefined to empty
+HWY_EXTRA_CONFIG ?=
+
 %:
 	dh $@ --buildsystem=cmake
 
 override_dh_auto_configure:
-	dh_auto_configure -- -DHWY_SYSTEM_GTEST=ON
+	dh_auto_configure -- -DHWY_SYSTEM_GTEST=ON $(HWY_EXTRA_CONFIG)