moved LDFLAGS to end of gcc invocation to fix build

Hi! I noticed that things weren't linking under Ubuntu 14.10, with the following error:

```
gcc -lm main.o parse.o include_file.o pass_1.o pass_2.o pass_3.o pass_4.o stack.o listfile.o -o wla-huc6280 ; strip wla-huc6280
pass_1.o: In function `parse_directive':
pass_1.c:(.text+0x9af5): undefined reference to `cos'
pass_1.c:(.text+0xa710): undefined reference to `sin'
collect2: error: ld returned 1 exit status
```

Apparently you have to put the -lm flag to gcc at the end, or the math libs won't be correctly linked. This patch adjusts the unix.* makefiles to move LDFLAGS and make everything build. I don't know if this fix is necessary on the other platforms, since I don't have them available for testing.