MIPS: Include missing mips16.S in libgcc/lib1funcs.S

mips16.S was missing since
commit 29b74545
Date:   Thu Jun 1 10:14:24 2023 +0800

    MIPS: Add speculation_barrier support

Without mips16.S included, some symbols will miss for mips16, and
so some software will fail to build.

libgcc/ChangeLog:

	* config/mips/lib1funcs.S: Includes mips16.S.