info gcc(section "Specifying subprocesses and the switches to pass to them"):
-Lor include dirs through
-I. For example to line:
/usr/local/libto linker options automatically.
In previous code you can see that when
-pg option (to profile program) passed gcc adds libgmon to linker, when
-mwindows passed gcc adds another libraries.
The specs file is no longer installed on most platforms because it buildin info gcc binary.
But you can still use it when specify it to gcc: