<hsroot>/common/autoconf/flags.m4 contains duplicated code to add -D__solaris__ to the JDK compiler flags when the target os is solaris.

719 if test "x$OPENJDK_TARGET_OS" = xsolaris; then
720 $2CFLAGS_JDK="${$2CFLAGS_JDK} -D__solaris__"
721 $2CXXFLAGS_JDK="${$2CXXFLAGS_JDK} -D__solaris__"
722 fi
723
724 if test "x$OPENJDK_TARGET_OS" = xsolaris; then
725 $2CFLAGS_JDK="${$2CFLAGS_JDK} -D__solaris__"
726 $2CXXFLAGS_JDK="${$2CXXFLAGS_JDK} -D__solaris__"
727 fi

I think we can dispense with lines 724-727.