host/lib/include/subprocess.h: Add `extern` to globals

This prevents linker errors regarding multiple definitions.

Change-Id: I62d6132c20ca2b9620a9f3b1539a1a0109c5aa26
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2318026
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Tested-by: Joel Kitching <kitching@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
1 file changed