Add dependency on google-sparsehash

CMakeModules/FindSparsehash.cmake

@@ -0,0 +1,25 @@
+# - Find google-sparsehash
+# Find the google-sparsehash includes
+# This module defines
+# SPARSEHASH_INCLUDE_DIR, root jreen include dir.
+# SPARSEHASH_FOUND, whether libjreen was found
+
+FIND_PACKAGE(PkgConfig QUIET)
+PKG_CHECK_MODULES(PC_SPARSEHASH QUIET libsparsehash)
+
+FIND_PATH(SPARSEHASH_INCLUDE_DIR NAMES google/sparsetable
+    HINTS
+        ${PC_SPARSEHASH_INCLUDEDIR}
+        ${PC_SPARSEHASH_INCLUDE_DIRS}
+        ${CMAKE_INSTALL_INCLUDEDIR}
+)
+
+IF(SPARSEHASH_INCLUDE_DIR AND NOT PC_SPARSEHASH_VERSION)
+    MESSAGE(WARNING "You don't have pkg-config and so the google-sparsehash version check does not work!")
+ENDIF()
+
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(Sparsehash
+    REQUIRED_VARS SPARSEHASH_INCLUDE_DIR)
+
+MARK_AS_ADVANCED(SPARSEHASH_INCLUDE_DIR)