Add "check-gcc-newlib" to run the GCC test suite

This also adds a submodule pointer to the RISC-V DejaGnu port, which is
required to run the GCC test suite.  The DejaGnu port only supports the
GDB simulator.  A bunch of tests fail right now, but that's expected.

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "riscv-glibc"]
 	path = riscv-glibc
 	url = ../riscv-glibc.git
+[submodule "riscv-dejagnu"]
+	path = riscv-dejagnu
+	url = ../riscv-dejagnu.git

Makefile.in

@@ -268,6 +268,13 @@ stamps/build-gcc-newlib: src/newlib-gcc stamps/build-binutils-newlib
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@
 
+.PHONY: check-gcc-newlib
+check-gcc-newlib: stamps/build-gcc-newlib
+	export PATH=$(INSTALL_DIR)/bin:$(PATH) && \
+	export DEJAGNULIBS=$(srcdir)/riscv-dejagnu && \
+	cd build-gcc-newlib && \
+	$(MAKE) check-gcc "RUNTESTFLAGS=--target_board=riscv-sim"
+
 clean:
 	rm -rf build-* $(addprefix src/,$(PACKAGES)) stamps
 

riscv-dejagnu

@@ -0,0 +1 @@
+Subproject commit 5f3adaf58af9bda05f63452323b4f7824da11d89