Fix lm32 makefile include paths

[shenki]

The current makefile links with ld directly, but depends on libc from GCC. To be able to link we hardcode the path to the libc.a:

LIBS = -L/opt/lm32/lm32-elf/lib -lc -L/opt/lm32/lib/gcc/lm32-elf/6.3.0 -lgcc

We depend on libc for setjmp, longjmp. As we don't need libgcc, we could drop the second part of this to not depend on the path of a specific GCC version.

However, we would prefer to use GCC to link.

[shenki]

This is mostly resolved with 015e480.

However, I still don't understand why we need to specify -lc on the command line.