Restore soname versioning with CMake build

Before:

$ readelf -d build/libleveldb.so | grep soname
 0x000000000000000e (SONAME)             Library soname: [libleveldb.so]

After:
$ readelf -d build/libleveldb.so | grep soname
 0x000000000000000e (SONAME)             Library soname: [libleveldb.so.1]

This matches the soname from v1.20.

PiperOrigin-RevId: 241334113

CMakeLists.txt

@@ -233,6 +233,10 @@ if(BUILD_SHARED_LIBS)
       # Used by include/export.h.
       LEVELDB_SHARED_LIBRARY
   )
+  set_target_properties(leveldb
+    PROPERTIES VERSION ${PROJECT_VERSION})
+  set_target_properties(leveldb
+    PROPERTIES SOVERSION 1)
 endif(BUILD_SHARED_LIBS)
 
 if(HAVE_CLANG_THREAD_SAFETY)