Add conditional debug build support to configure

Modifies configure script to optionally enable debug-related compile options:
 - --enable-debug
 - --enable-profiling
 - --enable-cassert
 - --enable-debug-extensions

These flags are enabled when ENABLE_DEBUG=true is set in the environment.
This provides flexibility to generate both debug and non-debug builds from
the same script, defaulting to non-debug builds.