Add a tock2 submodule with a tock-2.0-dev kernel, for use in integration tests.

tock2 will be removed when we are ready to delete Tock 1.x support.

.gitmodules

diff --git a/.gitmodules b/.gitmodules
index 45ddcde..d21db5e 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule "tock"]
 	path = tock
 	url = https://github.com/tock/tock.git
+[submodule "tock2"]
+	path = tock2
+	url = https://github.com/tock/tock.git

Makefile

diff --git a/Makefile b/Makefile
index da40d28..4f82d30 100644
--- a/Makefile
+++ b/Makefile
@@ -54,6 +54,14 @@
 	$(MAKE) -C tock/boards/hifive1 \
 		$(CURDIR)/tock/target/riscv32imac-unknown-none-elf/release/hifive1.elf
 
+# Builds a Tock 2.0 kernel for the HiFive board for use by QEMU tests.
+# TODO: After Tock 2.0 is released, we should merge the tock/ and tock2/
+# submodules and only build Tock 2.0 kernels.
+.PHONY: kernel-hifive-2
+kernel-hifive-2:
+	$(MAKE) -C tock2/boards/hifive1 \
+		$(CURDIR)/tock2/target/riscv32imac-unknown-none-elf/release/hifive1.elf
+
 # Prints out the sizes of the example binaries.
 .PHONY: print-sizes
 print-sizes: examples

tock2

diff --git a/tock2 b/tock2
new file mode 160000
index 0000000..17e698e
--- /dev/null
+++ b/tock2
@@ -0,0 +1 @@
+Subproject commit 17e698e8fb2c9628624398435f75db0f5a50dbcd