Fix builds that aren't in the top-level directory

I broke this with the binutils submodule.

Makefile.in

@@ -116,10 +116,10 @@ $(addprefix $(srcdir)/patches/,$(PACKAGES)): $(srcdir)/patches/%: src/%
 
 patches: $(addprefix $(srcdir)/patches/,$(PACKAGES))
 
-stamps/build-binutils-linux: riscv-binutils-gdb
+stamps/build-binutils-linux: $(srcdir)/riscv-binutils-gdb
 	rm -rf $@ $(notdir $@)
 	mkdir $(notdir $@)
-	cd $(notdir $@) && $(CURDIR)/$</configure \
+	cd $(notdir $@) && $</configure \
 		--target=riscv$(XLEN)-unknown-linux-gnu \
 		--prefix=$(INSTALL_DIR) \
 		--with-sysroot=$(SYSROOT) \
@@ -226,10 +226,10 @@ stamps/build-gcc-linux-stage2: src/gcc stamps/build-glibc-linux$(XLEN) \
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@
 
-stamps/build-binutils-newlib: riscv-binutils-gdb
+stamps/build-binutils-newlib: $(srcdir)/riscv-binutils-gdb
 	rm -rf $@ $(notdir $@)
 	mkdir $(notdir $@)
-	cd $(notdir $@) && $(CURDIR)/$</configure \
+	cd $(notdir $@) && $</configure \
 		--target=riscv$(XLEN)-unknown-elf \
 		--prefix=$(INSTALL_DIR) \
 		--enable-tls \