make.sh: Refactor XZ compression parameters again

I completely ruined this now and therefore I had to make
it new again:

* I split the parameters into smaller chunks now and added
  comments about why we have chosen those.

* I move it all to configure_build() since we do not need
  to check if the host architecture is 64 bit capable, but
  the architecture we are building for.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

make.sh

@@ -225,6 +225,30 @@ configure_build() {
 
 		MAKETUNING="-j${parallelism}"
 	fi
+
+	# Compression parameters
+	# We use mode 8 for reasonable memory usage when decompressing
+	# but with overall good compression
+	XZ_OPT="-8"
+
+	# We try to use as many cores as possible
+	XZ_OPT="${XZ_OPT} -T0"
+
+	# We need to limit memory because XZ uses too much when running
+	# in parallel and it isn't very smart in limiting itself.
+	# We allow XZ to use up to 70% of all system memory.
+	local xz_memory=$(( HOST_MEM * 7 / 10 ))
+
+	# XZ memory cannot be larger than 2GB on 32 bit systems
+	case "${build_arch}" in
+		i*86|armv*)
+			if [ ${xz_memory} -gt 2048 ]; then
+				xz_memory=2048
+			fi
+			;;
+	esac
+
+	XZ_OPT="${XZ_OPT} --memory=${xz_memory}MiB"
 }
 
 configure_build_guess() {
@@ -861,20 +885,6 @@ fi
 # Get the amount of memory in this build system
 HOST_MEM=$(system_memory)
 
-# We compress archives with "xz -8", using all cores and up to 70% of memory
-XZ_MEM=$(( HOST_MEM * 7 / 10 ))
-
-# XZ memory cannot be larger than 2GB on 32 bit systems
-case "${HOST_ARCH}" in
-	i*86|armv*)
-		if [ ${XZ_MEM} -gt 2048 ]; then
-			XZ_MEM=2048
-		fi
-		;;
-esac
-
-XZ_OPT="-T0 -8 --memory=${XZ_MEM}MiB"
-
 if [ -n "${BUILD_ARCH}" ]; then
 	configure_build "${BUILD_ARCH}"
 else