Mention --enable-optimize for --enable-debug

[bombless]

Closes #24840

[rust-highfive]

r? @nikomatsakis

(rust_highfive has picked a reviewer for you, use r? to override)

[pnkfelix]

Update: Moved content/rant to https://internals.rust-lang.org/t/why-is-enable-debug-implying-disable-optimize-for-rustc/1978

Sorry for the attempted hijack of the comment thread.

[pnkfelix]

(Arguably I really should not be using github comments for this argument and hijacking a well-meaning pull request like this, which is certainly an improvement over the status quo. I'll copy the above comment to an internals post instead.)

[pnkfelix]

First, grammatical typo: "as it disable optimization by default" is not correct. perhaps you meant "... it disables ..." ?

Second: Its pretty long; it gets out to column 114 in my editor, and so it will pretty long in the users terminal. I'm not sure if we have other help text for configure that is so long on one line.

Third: the word "it" in the output is slightly ambiguous; a naive user might think that the word "it" there refers to the --enable-optimize option. (Yes, i know that would be a silly interpretation.)

Maybe better text would be just:

"debug mode; disables optimization unless `--enable-optimize` given"

[bombless]

@pnkfelix , thanks for your patience :)

[pnkfelix]

@bors r+ 98b7aaf rollup

[bors]

⌛️ Testing commit 98b7aaf with merge 2f613bf...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-32-nopt-t, auto-win-32-opt, auto-win-64-nopt-t, auto-win-64-opt