fix static build

Add BUILD_SHARED_LIBS and BUILD_STATIC_LIBS to allow the user to build a
static only version

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

example/CMakeLists.txt

@@ -1,4 +1,9 @@
 include_directories(${CMAKE_SOURCE_DIR}/src ${CMAKE_SOURCE_DIR}/src/buffer ${CMAKE_BINARY_DIR}/src ${LIBEV_INCLUDE_DIR})
 
 add_executable(example example.c)
-target_link_libraries(example uhttpd ${LIBEV_LIBRARY})
+
+if(BUILD_SHARED_LIBS)
+    target_link_libraries(example uhttpd ${LIBEV_LIBRARY})
+else()
+    target_link_libraries(example uhttpd_s ${LIBEV_LIBRARY})
+endif()