Add generate and install rocksdb.pc file

Installed rocksdb.pc allows easy detection of the presence in
system image rocksdb devel resources for other project which want
to use rocksdb.pc.

Signed-off-by: Tomasz Kłoczko <kloczek@githug.com>

CMakeLists.txt

@@ -1125,6 +1125,11 @@ if(NOT WIN32 OR ROCKSDB_INSTALL_ON_WINDOWS)
 
   install(DIRECTORY "${PROJECT_SOURCE_DIR}/cmake/modules" COMPONENT devel DESTINATION ${package_config_destination})
 
+  configure_package_config_file(
+    ${CMAKE_CURRENT_LIST_DIR}/rocksdb.pc.in rocksdb.pc
+    INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+  )
+
   install(
     TARGETS ${ROCKSDB_STATIC_LIB}
     EXPORT RocksDBTargets
@@ -1159,6 +1164,13 @@ if(NOT WIN32 OR ROCKSDB_INSTALL_ON_WINDOWS)
     COMPONENT devel
     DESTINATION ${package_config_destination}
   )
+
+  install(
+    FILES
+    ${CMAKE_CURRENT_BINARY_DIR}/rocksdb.pc
+    COMPONENT devel
+    DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+  )
 endif()
 
 option(WITH_ALL_TESTS "Build all test, rather than a small subset" ON)

rocksdb.pc.in

@@ -0,0 +1,12 @@
+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=${prefix}
+libdir=@CMAKE_INSTALL_LIBDIR@
+includedir=${prefix}/include
+
+Name: @PROJECT_NAME@
+Description: @CMAKE_PROJECT_DESCRIPTION@
+URL: @CMAKE_PROJECT_HOMEPAGE_URL@
+Version: @PROJECT_VERSION@
+Cflags: -I${includedir}
+Libs: -L${libdir} -lrocksdb
+