gimp crashes for me during its initialization when it is querying 
plugins.  Running it under gdb shows that the crash occurs when gimp 
(via g_spawn_async) tries to fork a subprocess to run a plugin.

Rather than try to debug this further, I decided to build the latest 
gimp (2.10.0).  With this version of gimp, I get the error

   child_info_fork::abort: unable to map 
C:\cygwin64\bin\cygSDL-1-2-0.dll, Win32 error 1114

at the same point instead of an immediate crash.  Running gimp under 
strace produced the error message "fork: child 9396 - died waiting for 
dll loading, errno 11" instead of the "unable to map..." message.

Since cygSDL-1-2-0.dll is brought in via a libgegl package, I rebuilt 
the latter without SDL support, and that worked around the problem: gimp 
now finishes its initialization with no errors.

Note that the "unable to map..." error was recently reported for 
cygSDL2-2-0-0.dll in a different context:

   https://cygwin.com/ml/cygwin/2018-05/msg00207.html

At this point I'm stuck.  I don't know what would cause the "unable to 
map..." error.  Could it be something as simple as the libSDL* packages 
missing some dependencies?  I noticed that 'cygcheck 
/usr/bin/cygSDL-1-2-0.dll' shows no dependencies on Cygwin DLLs other 
than cygwin1.dll; all the dependencies of libSDL1.2_0 were added 
manually in the cygport file.

cygcheck output is attached.

Ken