Makefile: make out-of-source building possible.

It is now possible to use the BUILD variable to point make in the location
to use for building the binary dependencies. When installing the DIST env
variable can point make where to install protonfixes

Example usage in proton's makefile:

```
PROTONFIXES_OBJ = ./obj-protonfixes
PROTONFIXES_TARGET := $(addprefix $(DST_BASE)/,protonfixes)
$(PROTONFIXES_TARGET): $(addprefix $(SRCDIR)/,protonfixes)

$(OBJ)/.build-protonfixes:
	cd $(SRCDIR)/protonfixes && \
	env BUILD=$(PROTONFIXES_OBJ) make
	touch $(@)

$(PROTONFIXES_TARGET): $(OBJ)/.build-protonfixes
	cd $(SRCDIR)/protonfixes && \
	env BUILD=$(PROTONFIXES_OBJ) DIST=$(PROTONFIXES_TARGET) make install
```

Author: loathingKernel

Makefile

@@ -1,8 +1,13 @@
-OBJDIR      := builddir
-PREFIX      ?= /files
-LIBDIR       = $(PREFIX)/lib/x86_64-linux-gnu
-DESTDIR     ?=
-INSTALL_DIR ?= $(shell pwd)/dist/protonfixes
+BUILD ?= build
+DIST  ?= dist
+
+OBJDIR := $(shell realpath $(BUILD))
+DSTDIR := $(shell realpath $(DIST))
+TARGET_DIR := $(DSTDIR)/protonfixes
+
+BASEDIR       := /files
+i386_LIBDIR    = $(BASEDIR)/lib/i386-linux-gnu
+x86_64_LIBDIR  = $(BASEDIR)/lib/x86_64-linux-gnu
 
 .PHONY: all
 
@@ -21,14 +26,14 @@ install: protonfixes-install cabextract-install libmspack-install unzip-install
 
 protonfixes-install: protonfixes
 	$(info :: Installing protonfixes )
-	install -d              $(INSTALL_DIR)
-	cp      -r gamefixes-*  $(INSTALL_DIR)
-	cp      -r verbs        $(INSTALL_DIR)
-	cp         *.py         $(INSTALL_DIR)
-	mkdir   -p              $(INSTALL_DIR)/files/bin
-	cp         winetricks   $(INSTALL_DIR)/files/bin
-	cp         umu-database.csv   $(INSTALL_DIR)
-	rm $(INSTALL_DIR)/protonfixes_test.py
+	install -d              $(TARGET_DIR)
+	cp      -r gamefixes-*  $(TARGET_DIR)
+	cp      -r verbs        $(TARGET_DIR)
+	cp         *.py         $(TARGET_DIR)
+	mkdir   -p              $(TARGET_DIR)$(BASEDIR)/bin
+	cp         winetricks   $(TARGET_DIR)$(BASEDIR)/bin
+	cp         umu-database.csv   $(TARGET_DIR)
+	rm $(TARGET_DIR)/protonfixes_test.py
 
 #
 # libmspack and cabextract
@@ -45,7 +50,7 @@ $(OBJDIR)/.build-cabextract-dist: | $(OBJDIR)/libmspack
 	$(info :: Building cabextract )
 	cd $(OBJDIR)/libmspack/cabextract && \
 	autoreconf -fiv -I /usr/share/gettext/m4/ && \
-	./configure --prefix=$(PREFIX) --libdir=$(LIBDIR) && \
+	./configure --prefix=$(BASEDIR) --libdir=$(x86_64_LIBDIR) && \
 	make
 	touch $(@)
 
@@ -56,8 +61,8 @@ cabextract-dist: $(OBJDIR)/.build-cabextract-dist
 cabextract-install: cabextract-dist
 	$(info :: Installing cabextract )
 	cd $(OBJDIR)/libmspack/cabextract && \
-	make DESTDIR=$(INSTALL_DIR) install
-	rm -r $(INSTALL_DIR)/files/share
+	make DESTDIR=$(TARGET_DIR) install
+	rm -r $(TARGET_DIR)$(BASEDIR)/share
 
 #
 # libmspack
@@ -67,7 +72,7 @@ $(OBJDIR)/.build-libmspack-dist: | $(OBJDIR)/libmspack
 	$(info :: Building libmspack )
 	cd $(OBJDIR)/libmspack/libmspack && \
 	autoreconf -vfi && \
-	./configure --prefix=/files --libdir=/files/lib/x86_64-linux-gnu --disable-static && \
+	./configure --prefix=$(BASEDIR) --libdir=$(x86_64_LIBDIR) --disable-static && \
 	sed -i -e 's/ -shared / -Wl,-O1,--as-needed\0/g' libtool && \
 	make
 	touch $(@)
@@ -79,10 +84,10 @@ libmspack-dist: $(OBJDIR)/.build-libmspack-dist
 libmspack-install: libmspack-dist
 	$(info :: Installing libmspack )
 	cd $(OBJDIR)/libmspack/libmspack && \
-	make DESTDIR=$(INSTALL_DIR) install
-	rm -r $(INSTALL_DIR)/files/include
-	rm -r $(INSTALL_DIR)/files/lib/x86_64-linux-gnu/pkgconfig
-	rm    $(INSTALL_DIR)/files/lib/x86_64-linux-gnu/libmspack.la
+	make DESTDIR=$(TARGET_DIR) install
+	rm -r $(TARGET_DIR)$(BASEDIR)/include
+	rm -r $(TARGET_DIR)$(BASEDIR)/lib/x86_64-linux-gnu/pkgconfig
+	rm    $(TARGET_DIR)$(BASEDIR)/lib/x86_64-linux-gnu/libmspack.la
 
 #
 # unzip
@@ -102,7 +107,7 @@ $(OBJDIR)/.build-unzip-dist: | $(OBJDIR)
 	rsync -arx --delete subprojects/unzip $(OBJDIR)
 	cd $(OBJDIR)/unzip && \
 	$(foreach pch, $(UNZIP_PATCHES),patch -Np1 -i debian/patches/$(pch) &&) \
-	make -f unix/Makefile D_USE_BZ2=-DUSE_BZIP2 L_BZ2=-lbz2 LF2="$(LDFLAGS)" CF="$(CFLAGS) -I. $(DEFINES)" unzips
+	make -f unix/Makefile prefix=$(BASEDIR) D_USE_BZ2=-DUSE_BZIP2 L_BZ2=-lbz2 LF2="$(LDFLAGS)" CF="$(CFLAGS) -I. $(DEFINES)" unzips
 	touch $(@)
 
 .PHONY: unzip-dist
@@ -112,9 +117,9 @@ unzip-dist: $(OBJDIR)/.build-unzip-dist
 unzip-install: unzip-dist
 	$(info :: Installing unzip )
 	cd $(OBJDIR)/unzip && \
-	make -f unix/Makefile prefix=$(INSTALL_DIR)/files install
+	make -f unix/Makefile prefix=$(TARGET_DIR)$(BASEDIR) install
 	# Post install
-	rm -r $(INSTALL_DIR)/files/man
+	rm -r $(TARGET_DIR)$(BASEDIR)/man
 
 #
 # python-xlib
@@ -133,10 +138,10 @@ python-xlib-dist: $(OBJDIR)/.build-python-xlib-dist
 
 python-xlib-install: python-xlib-dist
 	$(info :: Installing python-xlib )
-	mkdir $(INSTALL_DIR)/_vendor
+	mkdir $(TARGET_DIR)/_vendor
 	cd $(OBJDIR)/python-xlib && mkdir dist && \
 	python setup.py install --root=dist --optimize=1 --skip-build && \
-	find dist -type d -name Xlib | xargs -I {} mv {} $(INSTALL_DIR)/_vendor; \
+	find dist -type d -name Xlib | xargs -I {} mv {} $(TARGET_DIR)/_vendor;
 
 $(OBJDIR):
 	@mkdir -p $(@)