Tell Git to always treat Makefile and build_odin.sh as Nix EOL

.gitattributes

@@ -1,2 +1,6 @@
 *.odin linguist-language=Odin
-* text=auto
+* text=auto
+
+# These files must always have *nix line-endings
+Makefile text eol=lf
+*.sh text eol=lf