Installing boost-spirit "properly"

Boost-spirit is not a self-contained library by any means,
unfortunately. Rather than inventing ad-hoc measures of installing the
dependencies and dependencies of dependencies and..., let's stop playing
whack-a-mole and instead use the big installation hammer.

We're not calling `b2 install` because that one attempts to build these
libraries. We do not want that. On the other hand, `b2 headers` is
"lazy" as it prefers to create symlinks where it makes sense. These
symlinks are relative, pointing to the source directory of each
individual Boost module -- hence that `cp`.

Yay for custom build systems, once again :(.

Change-Id: Iad867386ac5907630db8bdde0668d8fd9edee580
diff --git a/ci/do-build.sh b/ci/do-build.sh
index 1c0ca6b..891ebef 100755
--- a/ci/do-build.sh
+++ b/ci/do-build.sh
@@ -69,6 +69,12 @@
     do_test_dep_cmake spdlog -j${CI_PARALLEL_JOBS}
 
     # boost-spirit doesn't require installation
+    pushd ${TH_GIT_PATH}/submodules/boost
+    git submodule update --init
+    ./bootstrap.sh --prefix=${PREFIX}
+    ./b2 --ignore-site-config headers
+    cp -LR boost ${PREFIX}/include/
+    popd
 
     tar -C ~/target -cvJf ${TH_JOB_WORKING_DIR}/${ARTIFACT} .
     ssh th-ci-logs@ci-logs.gerrit.cesnet.cz mkdir -p artifacts/${TH_JOB_NAME} \