Fix issue that twice poac build will be succeeded even if code is corrupted

[wx257osn2]

Current poac skip entire build job if Makefile is up to date.
So, when we do poac build twice, second try must returns succeeded despite doing nothing.

$ poac new test
   Created binary (application) `
$ cd test/
$ echo "" > src/main.cc
$ poac build
 Compiling test v0.1.0 (/path/to/test)
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/14/../../../x86_64-linux-gnu/Scrt1.o: in function `_start':
(.text+0x1b): undefined reference to `main'
collect2: error: ld returned 1 exit status
make: *** [Makefile:21: /path/to/test/poac-out/debug/test] Error 1
Error: 'poac build' failed with exit code `2`
$ poac build
  Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s

This PR fixes this, and poac build will fail properly no matter how many times it's called.

[ken-matsui]

Would you mean the commands shown in your description are "what we should've seen", not "what we've seen"?

[wx257osn2]

Sorry for the lack of clarity in the description. Above code snipet is "What we've seen" (current poac behavior). This PR fixes it, so "what we should've seen" (poac behavior after merged this) will be build failure no matter how many times we try.

I've edited the PR description.