Z:gnu-gcl-templates--590cef-GCL now has optional support f/en

GCL now has optional support for profiling via gprof. Please see the documentation for si::gprof-start and si::gprof-quit for details. As this build is slower than builds without gprof support, it is not recommended for final production use. You can locally override the default choice made here by setting the GCL_PROF environment variable to any non-empty string for profiling support, and to the empty string for the more optimized builds, e.g. GCL_PROF=t gcl@EXT@. If profiling is enabled, this will be reported in the initial startup banner.