Linker warning recommends a nonexistant gcc::Config.fpic method

[Wallacoloo]

When using bindgen + gcc_rs to wrap bare metal C code, gcc_rs defaults to building with -fPIC, even though dynamic relocation never happens, making position independent code nonessential.

At link time when linking to a library built with -fPIC, the cortex-m-rt link script will error with:

.got section detected in the input files. Dynamic relocations are not
supported. If you are linking to C code compiled using the gcc crate
then modify your build script to compile the C code without the
-fPIC flag. See the documentation of the gcc::Config.fpic method for
details.

However, gcc::Config.fpic doesn't appear anywhere in the gcc-rs docs. The solution for me was to use the gcc::Config.flag method, passing it -fno-pic, e.g.

gcc::Build::new().flag("-fno-pic")

I'm not sure if I'm misunderstanding the warning or if it's outdated. If the latter, I tracked the error message down to here & I'm happy to make a PR that updates the message if requested.

[japaric]

It seems that Config has been renamed to Build in v0.3.51; Config is still around but it's deprecated. In any case, the message in wrong because the method's name is fpic, not pic. That should be fixed.

[japaric]

the message is wrong because the method's name is fpic, not pic

This has been fixed.