pkg/math: Add in more aliases in math.ll.

This makes "llgo-build -test math" link.
pkg/bytes: Implement bytes.Compare.

Makes "llgo-build -test bytes" link.
cmd/llgo-build: add "-work" flag.

This is mostly useful to keep the .o file around until there's a
proper solution for #82.
cmd/llgo-build: Use correct importpath when building a test binary.
cmd/llgo-build: Only add in functions starting with Test
Merge pull request #94 from quarnster/math

Various changes to make more tests linking