Bug 123786 Following bug 109980, the compliance 6.0 should be added to the compiler's compliance list.
If the JRE/JDK used is a 1.6/6.0 VM, then the compliance 6.0 should be available. Compliance 1.6 implies source level 1.6 and target level 1.6.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/ComplianceConfigurationBlock.java
String complianceLevel= getValue(PREF_COMPLIANCE);
		
		if (isDefault) {
			if (rememberOld) {
				if (oldComplianceLevel == null) {
					oldComplianceLevel= complianceLevel;
				}
				
				fRememberedUserCompliance[IDX_ASSERT_AS_IDENTIFIER]= getValue(PREF_PB_ASSERT_AS_IDENTIFIER);
				fRememberedUserCompliance[IDX_ENUM_AS_IDENTIFIER]= getValue(PREF_PB_ENUM_AS_IDENTIFIER);
				fRememberedUserCompliance[IDX_SOURCE_COMPATIBILITY]= getValue(PREF_SOURCE_COMPATIBILITY);
				fRememberedUserCompliance[IDX_CODEGEN_TARGET_PLATFORM]= getValue(PREF_CODEGEN_TARGET_PLATFORM);
				fRememberedUserCompliance[IDX_COMPLIANCE]= oldComplianceLevel;
			}
			if (VERSION_1_4.equals(complianceLevel)) {
				assertAsId= WARNING;
				enumAsId= WARNING;
				source= VERSION_1_3;
				target= VERSION_1_2;
			} else if (VERSION_1_5.equals(complianceLevel)) {
				assertAsId= ERROR;
				enumAsId= ERROR;
				source= VERSION_1_5;
				target= VERSION_1_5;
			} else {
				assertAsId= IGNORE;
				enumAsId= IGNORE;
				source= VERSION_1_3;
				target= VERSION_1_1;
			}