Auto merge of #30353 - alexcrichton:rpath-by-default, r=brson

Auto merge of #30353 - alexcrichton:rpath-by-default, r=brson

This commit changes our distribution and in-tree sources to pass the `-C rpath`
flag by default during compiles. This means that from-source builds, including
our release channels, will have this option enabled as well. Motivated
by #29941, this change means that the compiler should be usable as-is on all
platforms just after extraction or installation. This experience is already true
on Windows but on Unixes you still need to set up LD_LIBRARY_PATH or the
equivalent, which can often be unfortunate.

This option was originally turned off by default for Linux distributions who
tend to take care of these sorts of details themselves, so it is expected that
all those builds of Rust will want to pass `--disable-rpath` to the configure
script to preserve that behavior.

Closes #29941