Small Abseil fixes for dependents. (#1711)

Enable PIC so that shared libraries can use the Cartographer
library.

Fixes the config so that dependent builds can find Abseil.

Signed-off-by: Wolfgang Hess <whess@lyft.com>

cartographer-config.cmake.in

@@ -39,7 +39,7 @@ find_package(Ceres ${QUIET_OR_REQUIRED_OPTION} HINTS ${CERES_DIR_HINTS})
 if (WIN32)
     find_package(glog REQUIRED)
 endif()
-find_package(Abseil ${QUIET_OR_REQUIRED_OPTION})
+find_package(absl ${QUIET_OR_REQUIRED_OPTION})
 if(CARTOGRAPHER_HAS_GRPC)
    find_package(async_grpc ${QUIET_OR_REQUIRED_OPTION})
 endif()

docs/source/index.rst

@@ -71,6 +71,10 @@ On Ubuntu 16.04 (Xenial):
   :language: bash
   :lines: 20-
 
+.. literalinclude:: ../../scripts/install_abseil.sh
+  :language: bash
+  :lines: 20-
+
 .. literalinclude:: ../../scripts/install_ceres.sh
   :language: bash
   :lines: 20-

scripts/install_abseil.sh

@@ -24,6 +24,7 @@ mkdir build
 cd build
 cmake -G Ninja \
   -DCMAKE_BUILD_TYPE=Release \
+  -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
   -DCMAKE_INSTALL_PREFIX=/usr/local/stow/absl \
   ..
 ninja