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 collectible 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.

Incremental collection support was added recently, and should now work.

In spite of past claims, pthread support under HP/UX 11 should now work.
Define GC_THREADS macro for the build.  Incremental collection still does not
work in combination with it.

The stack finding code can be confused by putenv calls before collector
initialization.  Call GC_malloc() or GC_INIT() before any putenv() calls.
