Patch by Larry Doolittle to allow out-of-source builds of ABC.

Usage:

Starting from an empty directory:

(1) set AS to point to the location of ABC

(2) reconstruct the directory structure of ABC in the new directory:

    mkdir -p `cd $AS && find src -type d`

(3) Build ABC:

    make -f $AS/Makefile VPATH=$AS ABCSRC=$AS

Makefile

@@ -4,6 +4,7 @@ CXX  := g++
 LD   := $(CXX)
 
 MSG_PREFIX ?=
+ABCSRC = .
 
 $(info $(MSG_PREFIX)Using CC=$(CC))
 $(info $(MSG_PREFIX)Using CXX=$(CXX))
@@ -39,9 +40,9 @@ ARCHFLAGS_EXE ?= ./arch_flags
 $(ARCHFLAGS_EXE) : arch_flags.c
 	$(CC) arch_flags.c -o $(ARCHFLAGS_EXE)
 
-INCLUDES += -Isrc
+INCLUDES += -I$(ABCSRC)/src
 
-ARCHFLAGS ?= $(shell $(CC) arch_flags.c -o $(ARCHFLAGS_EXE) && $(ARCHFLAGS_EXE))
+ARCHFLAGS ?= $(shell $(CC) $(ABCSRC)/arch_flags.c -o $(ARCHFLAGS_EXE) && $(ARCHFLAGS_EXE))
 ARCHFLAGS := $(ARCHFLAGS)
 
 OPTFLAGS  ?= -g -O
@@ -135,7 +136,7 @@ GARBAGE := core core.* *.stackdump ./tags $(PROG) arch_flags
 
 .PHONY: all default tags clean docs cmake_info
 
-include $(patsubst %, %/module.make, $(MODULES))
+include $(patsubst %, $(ABCSRC)/%/module.make, $(MODULES))
 
 OBJ := \
 	$(patsubst %.cc, %.o, $(filter %.cc, $(SRC))) \
@@ -163,15 +164,15 @@ DEP := $(OBJ:.o=.d)
 
 %.d: %.c
 	@echo "$(MSG_PREFIX)\`\` Generating dependency:" $(LOCAL_PATH)/$<
-	$(VERBOSE)./depends.sh $(CC) `dirname $*.c` $(OPTFLAGS) $(INCLUDES) $(CFLAGS) $*.c > $@
+	$(VERBOSE)$(ABCSRC)/depends.sh $(CC) `dirname $*.c` $(OPTFLAGS) $(INCLUDES) $(CFLAGS) $< > $@
 
 %.d: %.cc
 	@echo "$(MSG_PREFIX)\`\` Generating dependency:" $(LOCAL_PATH)/$<
-	$(VERBOSE)./depends.sh $(CXX) `dirname $*.cc` $(OPTFLAGS) $(INCLUDES) $(CXXFLAGS) $*.cc > $@
+	$(VERBOSE)$(ABCSRC)/depends.sh $(CXX) `dirname $*.cc` $(OPTFLAGS) $(INCLUDES) $(CXXFLAGS) $< > $@
 
 %.d: %.cpp
 	@echo "$(MSG_PREFIX)\`\` Generating dependency:" $(LOCAL_PATH)/$<
-	$(VERBOSE)./depends.sh $(CXX) `dirname $*.cpp` $(OPTFLAGS) $(INCLUDES) $(CXXFLAGS) $*.cpp > $@
+	$(VERBOSE)$(ABCSRC)/depends.sh $(CXX) `dirname $*.cpp` $(OPTFLAGS) $(INCLUDES) $(CXXFLAGS) $< > $@
 
 ifndef ABC_MAKE_NO_DEPS
 -include $(DEP)