compiletest: Only trim the end of process output

[Zalathar]

As of #94196, compiletest automatically trims process stderr/stdout output before printing it, to make failure info more compact.

This causes the first line of run-coverage output to be displayed incorrectly, because it uses leading whitespace to align line numbers.

Trimming only the end of the output string should still have the intended effect (e.g. removing trailing newlines), without causing problems for output that deliberately uses leading whitespace on the first line.

Before

--- stdout -------------------------------
1|      1|fn main() { //
    2|      1|    let num = 9;
    3|      1|    while num >= 10 {
    4|      0|    }
    5|      1|}
------------------------------------------
stderr: none

After

--- stdout -------------------------------
    1|      1|fn main() { //
    2|      1|    let num = 9;
    3|      1|    while num >= 10 {
    4|      0|    }
    5|      1|}
------------------------------------------
stderr: none

[rustbot]

r? @ozkanonur

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[onur-ozkan]

@bors r+ rollup

[bors]

📌 Commit 115cfda has been approved by ozkanonur

It is now in the queue for this repository.