javacomp: Silence -Wanalyzer-possible-null-argument warning. * lib/javacomp.c: Include verify.h. (is_envjavac_gcj43_usable, is_envjavac_oldgcj_14_13_usable, is_envjavac_nongcj_usable, compile_java_class): Assert that the xasprintf results are non-NULL. This is possible since all involved format strings are valid and don't use %ls, and all argument strings are small compared to INT_MAX. * modules/javacomp (Depends-on): Add verify.