Add libunwind.

.gitmodules

@@ -10,3 +10,6 @@
 [submodule "extcores/litepcie_phy_wrappers"]
 	path = extcores/litepcie_phy_wrappers
 	url = https://github.com/enjoy-digital/litepcie_phy_wrappers
+[submodule "software/unwinder"]
+	path = software/unwinder
+	url = https://github.com/whitequark/libunwind

software/libunwind/Makefile

@@ -0,0 +1,30 @@
+MSCDIR=../..
+include $(MSCDIR)/software/common.mak
+
+COMMONFLAGS+=-integrated-as \
+	-I. -I$(MSCDIR)/software/include/dyld/ -I$(MSCDIR)/software/unwinder/include/ \
+	-D__ELF__ -D__linux__
+
+OBJECTS=UnwindRegistersSave.o UnwindRegistersRestore.o UnwindLevel1.o libunwind.o
+
+all: libunwind.a
+
+# pull in dependency info for *existing* .o files
+-include $(OBJECTS:.o=.d)
+
+libunwind.a: $(OBJECTS)
+	$(AR) crs libunwind.a $(OBJECTS)
+
+%.o: $(MSCDIR)/software/unwinder/src/%.cpp
+	$(compilexx-dep)
+
+%.o: $(MSCDIR)/software/unwinder/src/%.c
+	$(compile-dep)
+
+%.o: $(MSCDIR)/software/unwinder/src/%.S
+	$(assemble)
+
+.PHONY: clean
+
+clean:
+	$(RM) $(OBJECTS) $(OBJECTS:.o=.ts) $(OBJECTS:.o=.d) libuwind.a .*~ *~

software/libunwind/strings.h

@@ -0,0 +1,2 @@
+// This is some obsolete BSD crap that libunwind pulls in
+// that's so old and useless it's not worth putting into libbase.

software/unwinder

@@ -0,0 +1 @@
+Subproject commit 7ce966d59aa6c5a8b962dca43a34279b69bec597