[oe] [meta-java] gcc6 support breaks build for gcc < 6

[Winfried]

Commit 	33ddb28a6428b02ddcc82d1954ecf27cd426fbb5 (openjdk-8: make GCC6 
happy) adds gcc option -fno-lifetime-dse, which was added in gcc6. This 
breaks the compilation of openjdk-native on hosts where gcc4 or gcc5 is 
the default compiler.

If this is intentional, I think the README file should mention that 
meta-java requires gcc6. Better would be to add the '-fno-lifetime-dse' 
option only if gcc >= 6 is used for native compilation (if that is 
possible).

regards,
W. Dobbe