[8u] hotspot debug information not being built

We seem to have broken the creation of debuginfo bits in the jdk8u releases.

We get valid debuginfo bundles, including libjvm.diz or libjvm.debuginfo, but that file looks like it contains only libstdc++ content, nothing else.... The files are very small, e.g. 2 or 3 MB, not the >100MB we expect for the hotspot DWARF info.

The libjvm.debuginfo contains nothing describing source files in the hotspot repo.

Happened in jdk8u192-b07, b06 was good.
8u191-b12 is also bad.

Test with:
hg update all sub repos to e.g. jdk8u181-b37
bash configure --enable-debug-symbols
make clean images
ls -lah build/linux-x86_64-normal-server-release/images/j2sdk-image/jre/lib/amd64/server/libjvm.diz

...and check file size. The .diz is zipped, and can be around 835K with the problem, or 147MB without the problem.

Suspect https://bugs.openjdk.java.net/browse/JDK-8033251 made the key change. After updating repos to an older tag, cd hotspot and "hg udpate 8844:2af8917ffbee" causes the problem, hg update to one change before and debuginfo files are large again.