javacomp-script, javacomp: Add support for Java 11. * m4/javacomp.m4 (gt_JAVACOMP): Accept source-version 11 and target-version 11. * lib/javaversion.h: Update comments. * lib/javacomp.c (default_target_version, SOURCE_VERSION_BOUND, source_version_index, get_goodcode_snippet, get_failcode_snippet, TARGET_VERSION_BOUND, target_version_index, corresponding_classfile_version): Accept source_version 11 and target_version 11. * lib/javacomp.h: Update comments accordingly.