RFR (XS) 8202014: Possible to receive signal before signal semaphore created

[coleen.phillimore at oracle.com]

Summary: Don't assert for null semaphore because it can be null before 
initialization is complete.

Tested this with a shell script, thanks Robbin, and mach5 tier1,2 all 
Oracle platforms.  AIX doesn't use the semaphore class so doesn't have 
this bug.

open webrev at http://cr.openjdk.java.net/~coleenp/8202014.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8202014

Thanks,
Coleen