Remove linker option -pie since that option is only used when building (#882)

executables not shared libraries. This change will remove the following
warning.
ld: warning: -pie being ignored. It is only used when linking a main executable

CMakeLists.txt

@@ -126,7 +126,6 @@ set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wformat -Wformat-security")
 if (NOT APPLE)
     set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -z noexecstack")
     set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -z relro -z now")
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -pie")
 endif()
 if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
     if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9)