How can I change g++ options while compiling a Pin tool? For example, is it possible to prevent warnings from being treated as errors or is it possible to link the tool with an external library such as bfd?
Linking Pin to precompiled libraries is discouraged. Pin uses a different libc and linking will either fail or cause issues while running. If you wish to use an external library either compile it against pin's runtime or use it in a separate process.
To build specific files in a nonstandard way, add a rule to the Build rules section of the relevant makefile.
In general it is a bad idea to modify pin's default flags. They all serve a purpose.