Stop installing native extension build logs - #9700

Clean up the per-gem mkmf.log and gem_make.out left in build_info by a
failed extension build when the gem is uninstalled.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

These specs read the `make -jN` command line from `gem_make.out`, which a
successful build no longer writes. The integration specs in `install_spec`
now force the build to fail so the command lands in `build_info`, and the
`parallel_installer` specs assert on the number of jobserver slots each
gem's build acquired, which is exactly what becomes `make -jN`, instead of
reading a build log.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Older system RubyGems writes the build log to the extension directory, so
under RGV=system the example read the new build_info path and hit ENOENT.
The `-j` suppression it verifies only exists with the jobserver support in
RubyGems 4.1, so gate it like its sibling examples.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

build_info entries are matched by stripping ".info", so the new
<full_name>.mkmf.log and <full_name>.gem_make.out never matched an
installed gem and were removed as strays, including the log the build
error had just told the user to read. Let a subdirectory declare several
suffixes and give build_info all three.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Logs for a git source land in bundler/gems/build_info, which `bundle
clean` globs as a git checkout and reports as "Removing  (build_info)"
before deleting it. Exclude it the way the sibling extensions directory
already is.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Preserving a log happens while a build failure is being reported, so a
filesystem error there replaced the compile output the user needed with a
bare Errno, and the extension builder stopped raising Gem::Ext::BuildError
at all. Callers only rescue the Gem::InstallError family, so the failure
escaped as an unhandled exception. Swallow errors from moving mkmf.log and
from writing gem_make.out, and drop the "Results logged to" line when there
is no log to point at.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

An extconf that exits cleanly without generating a Makefile leaves the
extension unbuilt while the install still reports success. That case used
to be described in gem_make.out; since the success path stopped writing one
it went unrecorded entirely. Let the no-Makefile case reach
Gem::Ext::Builder, which already owns where logs end up, and have it write
the explanation to build_info.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

base_dir for a git source points at the directory holding every checkout, so
logs keyed by full_name collided between revisions of the same gem and landed
in bundler/gems/build_info, which nothing prunes and which `bundle clean`
mistook for a stale checkout. Resolve them from extension_dir instead, which
Bundler already makes unique per revision and which `bundle clean` removes
along with the checkout. That also drops the clean exclusion added for the
directory this no longer creates.

Path sources are unaffected: Bundler installs them with extensions disabled,
so they never produce a build log.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

The git extension spec overwrote the C source after build_git had already
committed the checkout, so bundle installed the original working source and
the build succeeded, leaving no log to find. Write the broken source inside
the build_git block, and assert the log is the one this failure produced.

ExtConfBuilder no longer swallows NoMakefileError, so on JRuby, where the
fixture extconf returns before creating a Makefile, calling the class method
directly now raises instead of returning.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

Where a build log goes is decided by the RubyGems running the install, and
under RGV=system that is an older one which writes a bare gem_make.out into
the extension directory. Gate the example the way the other specs that assert
on log locations already are.

Co-Authored-By: Claude Opus 4.8 <[email protected]>