No, that won't decrease your executable file size at all.
If I recall correctly, the linker will only link into your program the stuff it actually needs in order for it to be able to run.
Or at least I think that's the case with .a static libraries.
(not sure about .o object files, though)
If you want to decrease the size of your executable files, here are a few things I can think of (assuming you're using GCC):
-- Strip your executable using strip <my_exe_name_here>.exe or by compiling with -s
-- Try dynamic linking with -shared-libgcc -shared-libstdc++.
-- Compile with -Os if you really care about file size that much.
-- If you don't use dynamic_cast in your code, I heard somewhere that using -fno-rtti will shave off some bytes off of your final executable.
-- Use something like UPX to compress your executable.