Install pyelftools before testing

We use some non-standard python package in #1233, so we must make sure
it available before run the test.

Fix #1252

Makefile.in

@@ -178,7 +178,7 @@ report-gdb: report-gdb-@default_target@
 ifeq ($(SIM),qemu)
 SIM_PATH:=$(srcdir)/scripts/wrapper/qemu:$(srcdir)/scripts
 SIM_PREPARE:=PATH="$(SIM_PATH):$(INSTALL_DIR)/bin:$(PATH)" RISC_V_SYSROOT="$(SYSROOT)"
-SIM_STAMP:= stamps/build-qemu
+SIM_STAMP:= stamps/build-qemu stamps/install-python-package
 else
 ifeq ($(SIM),spike)
 # Using spike simulator.
@@ -872,6 +872,10 @@ stamps/build-pk64: $(PK_SRCDIR) stamps/build-gcc-newlib-stage2
 	mkdir -p $(dir $@)
 	date > $@
 
+stamps/install-python-package:
+	python3 -m pip install --user pyelftools
+	date > $@
+
 stamps/build-qemu: $(QEMU_SRCDIR) $(QEMU_SRC_GIT)
 	rm -rf $@ $(notdir $@)
 	mkdir $(notdir $@)