Cygwin: testsuite: link cygload with --disable-high-entropy-va

 Cygwin: testsuite: link cygload with --disable-high-entropy-va
 
 This is a mingw program meant to demonstrate loading the Cygwin dll in a
 non-Cygwin process, but the Cygwin dll still initializes the cygheap on
 load in that case.  Without --disable-high-entropy-va, Windows may
 occasionally locate the PEB, TEB, and/or stacks in the address space
 that Cygwin tries to reserve for the cygheap, resulting in a failure.
 
 Fixes: 60675f1a7eb2 ("Cygwin: decouple shared mem regions from Cygwin DLL")
 Signed-off-by: Jeremy Drake <cygwin@jdrake.com>