Auto-detect platform in makefiles and test runner

Use uname -s to select Linux vs macOS build flags instead of
hardcoding. Add -undefined dynamic_lookup for test shared libs
on macOS. Set _port=true automatically on non-Linux in ./all.

all

@@ -2,7 +2,11 @@ make -s -j
 cd testes/libs; make -s
 cd ..     # back to directory 'testes'
 ulimit -S -s 1100
-if { ../lua -W all.lua; } then
+LUA_FLAGS="-W"
+if [ "$(uname)" != "Linux" ]; then
+  LUA_FLAGS="$LUA_FLAGS -e_port=true"
+fi
+if { ../lua $LUA_FLAGS all.lua; } then
   echo -e "\n\n    final OK!!!!\n\n"
 else
   echo -e "\n\n    >>>> BUG!!!!\n\n"