Auto merge of #74540 - alexcrichton:std-no-backtrace, r=Mark-Simulacrum
Auto merge of #74540 - alexcrichton:std-no-backtrace, r=Mark-Simulacrum

std: Fix compilation without backtrace feature

This should hopefully handle #74484 but in any case fixes compilation of
the standard library without the `backtrace` feature. The need for this
feature is somewhat unclear now because the `backtrace` crate should
always compile (no more C code!) but we can handle that later if
necessary.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust