Only set DEB_BUILD_OPTIONS and DEB_BUILD_PROFILES for cross-building …

…when unset

Adapted from sbuild.

README.md

@@ -120,6 +120,12 @@ cross-building (cross-compilation) is automatically set up with `apt-get` and
 `dpkg-buildpackage` as described
 [in the Debian wiki](https://wiki.debian.org/CrossCompiling#Building_with_dpkg-buildpackage).
 
+To override their automatic cross-compilation setup, pass `CONFIG_SITE`,
+`DEB_BUILD_OPTIONS` or `DEB_BUILD_PROFILES` as an environment variable to the
+action with an empty or the desired value. The usual parameter(s) for
+cross-compilation, i.e., the path of a `cross-config.*` file, `nocheck` or
+`cross`, will **not** be assigned to the respective, given variable.
+
 Optional and defaults to the architecture the action is run on (likely amd64).
 
 Basic example for a cross-build:

scripts/build_packages

@@ -7,8 +7,12 @@ if [ -n "$INPUT_HOST_ARCH" ]; then
 	if [ -z "${CONFIG_SITE-}" ]; then
 		export CONFIG_SITE="/etc/dpkg-cross/cross-config.$INPUT_HOST_ARCH"
 	fi
-	export DEB_BUILD_OPTIONS="${DEB_BUILD_OPTIONS:+$DEB_BUILD_OPTIONS }nocheck"
-	export DEB_BUILD_PROFILES="${DEB_BUILD_PROFILES:+$DEB_BUILD_PROFILES }cross nocheck"
+	if [ -z "${DEB_BUILD_OPTIONS-}" ]; then
+		export DEB_BUILD_OPTIONS='nocheck'
+	fi
+	if [ -z "${DEB_BUILD_PROFILES-}" ]; then
+		export DEB_BUILD_PROFILES='cross nocheck'
+	fi
 	INPUT_BUILDPACKAGE_OPTS="$INPUT_BUILDPACKAGE_OPTS --host-arch=$INPUT_HOST_ARCH"
 fi