build-infra: mismatch with full debug symbol control for hotspot

In the old build the external variable that should be set to control Full Debug Symbols ( FDS) is FULL_DEBUG_SYMBOLS=0/1. This is turn will set the internal make variable ENABLE_FULL_DEBUG_SYMBOLS=0/1. This applies to JDK builds and hotspot builds, with the top-level build adding FULL_DEBUG_SYMBOLS to the HOTSPOT_BUILD_ARGUMENTS.

But in the new build the variable that is modified based onthe configure option --disable-debug-symbols is ENABLE_DEBUG_SYMBOLS=yes/no. So hotspot will read spec.gmk and only find ENABLE_DEBUG_SYMBOLS:=no, for example, but that has no affect on FDS as it expects FULL_DEBUG_SYMBOLS to control things.