Dynamic loading support requires that executables be linked with -ldld.
The alternative is to build the collector without defining DYNAMIC_LOADING
in gcconfig.h and ensuring that all garbage collectable objects are
accessible without considering statically allocated variables in dynamic
libraries.

The collector should compile with either plain cc or cc -Ae.  CC -Aa
fails to define _HPUX_SOURCE and thus will not configure the collector
correctly.

There is currently no thread support.
