Convert --toolchain_resolution_debug to take a regex of toolchain typ…

…es to debug

Work towards #12110.
Fixes #7713.

RELNOTES: The flag `--toolchain_resolution_debug` now takes a regex argument, which is used to check which toolchain types should have debug info printed. You may use `.*` as an argument to keep the current behavior of debugging every toolchain type.

Closes #13207.

PiperOrigin-RevId: 362413466

site/docs/user-manual.html

diff --git a/site/docs/user-manual.html b/site/docs/user-manual.html
index a348edf..21c69a7 100644
--- a/site/docs/user-manual.html
+++ b/site/docs/user-manual.html
@@ -1627,11 +1627,12 @@
   register_toolchains()</a>.
 </p>
 
-<h4 id="flag--toolchain_resolution_debug"><code class='flag'>--toolchain_resolution_debug=false</code></h4>
+<h4 id="flag--toolchain_resolution_debug"><code class='flag'>--toolchain_resolution_debug=<var>regex</var></code></h4>
 <p>
-  Print debug information while finding toolchains for a rule. This might help
-  developers of Bazel or Starlark rules with debugging failures due to missing
-  toolchains.
+  Print debug information while finding toolchains if the toolchain type matches
+  the regex. Multiple regexes can be separated by commas. The regex can be
+  negated by using a <code>-</code> at the beginning. This might help developers
+  of Bazel or Starlark rules with debugging failures due to missing toolchains.
 </p>
 
 <h3 id='misc_build_options'>Miscellaneous</h3>