mksh: stop loading libc++ and libm.

The dynamic linker unconditionally adds libdl, so this isn't quite down
to just libc, but it's as close as I can get from here.

Unfortunately my timings are in the noise so I can't prove that this
makes any difference in practice, but it can't *hurt*, so....

Test: ldd `which sh`
Change-Id: I9d864120e38d55c85c655ddeaba997cb20e42c6e
1 file changed