Use the downloaded clang when building for armhf-debian

This makes it work on a barebones Stretch installation.

Also add building for this CPU to the CI script so we know it keeps
working, which means marking everything that's supposed to work
appropriately.

Change-Id: Ic050ce20eae45c6b23e0e42dddb24db3ebc70b84
diff --git a/tools/cpp/linaro_linux_gcc/arm-linux-gnueabihf-gcc b/tools/cpp/linaro_linux_gcc/arm-linux-gnueabihf-gcc
index c70d6b3..71dd060 100755
--- a/tools/cpp/linaro_linux_gcc/arm-linux-gnueabihf-gcc
+++ b/tools/cpp/linaro_linux_gcc/arm-linux-gnueabihf-gcc
@@ -1,5 +1,9 @@
 #!/bin/bash --norc
 
+LD_LIBRARY_PATH="${BAZEL_OUTPUT_ROOT}external/linaro_49_deps/usr/lib/x86_64-linux-gnu"
+LD_LIBRARY_PATH+=":${BAZEL_OUTPUT_ROOT}external/linaro_49_deps/lib/x86_64-linux-gnu"
+export LD_LIBRARY_PATH
+
 PATH="${BAZEL_OUTPUT_ROOT}external/linaro_linux_gcc_4_9_repo/libexec/gcc/arm-linux-gnueabihf/4.9.3:$PATH" \
 	exec \
 	${BAZEL_OUTPUT_ROOT}external/linaro_linux_gcc_4_9_repo/bin/arm-linux-gnueabihf-gcc \