--- Makefile.orig	2020-02-09 08:53:36 UTC
+++ Makefile
@@ -18,17 +18,17 @@
 # along with this program; if not, write to the Free Software
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
 
-PREFIX = /usr
+PREFIX ?= /usr
 BINDIR = $(PREFIX)/bin
 DATADIR = $(PREFIX)/share
-DESTDIR =
+DESTDIR ?=
 CROSS =
 
 BOOST_TAGS := $(if $(filter %-w64-mingw32.static-,$(CROSS)),-mt,)
 CONVERT = convert
-CXX = $(CROSS)$(CXX_NATIVE)
-CXX_NATIVE = g++
-CXXFLAGS = -Wall -Wextra -g -O2 -std=c++17
+CXX ?= $(CROSS)$(CXX_NATIVE)
+CXX_NATIVE = ${CXX}
+CXXFLAGS += -Wall -Wextra -std=c++17
 EXEEXT = $(if $(filter %-w64-mingw32.static-,$(CROSS)),.exe,)
 INSTALL = install
 LDFLAGS =
@@ -129,7 +129,7 @@ FILES_DATADIR += data/icons/hicolor/48x48/apps/domino-
 FILES_DATADIR += data/icons/hicolor/64x64/apps/domino-chain.png
 data/icons/hicolor/%/apps/domino-chain.png: src/doc/domino-chain.ico
 	@mkdir -p $(dir $@)
-	$(CONVERT) +set date:create +set date:modify $<[$(shell expr substr $* 1 2 / 16 - 1)] $@
+	$(CONVERT) +set date:create +set date:modify $<[$(shell expr $$(echo $* | cut -b 1-2) / 16 - 1)] $@
 
 DOC_INCLUDES += src/doc/upload-url-dist-windows
 
@@ -182,7 +182,6 @@ _tmp/po/leveltexts.cpp: src/levels/*/*.level
 	@mkdir -p $(dir $@)
 	sed -n '/^\(Description\|Hint\|Name\|Tutorial\)$$/,/^[^|]/ s,^| \(.*\)$$,_("\1"),p' src/levels/*/*.level | LC_ALL=C sort -u >$@
 
-FILES_DATADIR_SYS += data/fonts/FreeSans.ttf
 data/fonts/FreeSans.ttf:
 	@mkdir -p $(dir $@)
 	if [ -e /usr/share/fonts/truetype/freefont/FreeSans.ttf ]; then cp /usr/share/fonts/truetype/freefont/$(notdir $@) $@; \