Add option to disable remap-path-prefix option to be added to rustc

[jeffy1009]

Bazel rules for rust seems to remove path-prefix by default for build determinism, but it is disturbing when GDB debugging since I have to manually teach GDB the source locations for Rust source code, external crates, etc.

rules_rust/rust/private/rustc.bzl

Lines 954 to 955 in d680d81

	if remap_path_prefix != None:
	rustc_flags.add("--remap-path-prefix=${{pwd}}={}".format(remap_path_prefix))

It would be useful to have an option to disable the behavior locally, e.g., in .bazelrc