Add --gc-sections to LDFLAGS.

Add --gc-sections to LDFLAGS.

This, together with -fdata-sections and -ffunction-sections brought
nice size reductions. Before:

-rwxr-xr-x 1 maan fml  29K Oct 11 14:32 para_audioc*
-rwxr-xr-x 1 maan fml  42K Oct 11 14:32 para_client*
-rwxr-xr-x 1 maan fml  33K Oct 11 14:32 para_fade*
-rwxr-xr-x 1 maan fml  38K Oct 11 14:32 para_filter*
-rwxr-xr-x 1 maan fml  54K Oct 11 14:32 para_fsck*
-rwxr-xr-x 1 maan fml  52K Oct 11 14:32 para_gui*
-rwxr-xr-x 1 maan fml  42K Oct 11 14:32 para_recv*
-rwxr-xr-x 1 maan fml 216K Oct 11 14:32 para_server*
-rwxr-xr-x 1 maan fml  38K Oct 11 14:32 para_write*

After:

-rwxr-xr-x 1 maan fml  21K Oct 11 14:31 para_audioc*
-rwxr-xr-x 1 maan fml  33K Oct 11 14:31 para_client*
-rwxr-xr-x 1 maan fml  29K Oct 11 14:31 para_fade*
-rwxr-xr-x 1 maan fml  29K Oct 11 14:31 para_filter*
-rwxr-xr-x 1 maan fml  45K Oct 11 14:31 para_fsck*
-rwxr-xr-x 1 maan fml  47K Oct 11 14:31 para_gui*
-rwxr-xr-x 1 maan fml  30K Oct 11 14:31 para_recv*
-rwxr-xr-x 1 maan fml 208K Oct 11 14:31 para_server*
-rwxr-xr-x 1 maan fml  29K Oct 11 14:31 para_write*