configure: java 20 removed support for 7/1.7 source, target, and release Values

Adding support for target 8 and adding related detection for java 20+ allows building with java 20 and 21. java 22 supports target 8 but fails to build. The is is the patch I used to test target 8:

diff --git a/Makefile.am b/Makefile.am
index 24b60f78..edc1ec43 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -241,6 +241,9 @@ pkginclude_HEADERS = \
 
 if USING_BDJAVA_BUILD_JAR
 
+if USING_JAVAC_20
+java_versions = -Djava_version_asm=1.8 -Djava_version_bdj=1.8
+else
 if USING_JAVAC_12
 java_versions = -Djava_version_asm=1.7 -Djava_version_bdj=1.7
 else
@@ -250,6 +253,7 @@ else
 java_versions = -Djava_version_asm=1.5 -Djava_version_bdj=1.4
 endif
 endif
+endif
 
 if BDJ_J2SE
 awt_src = java-$(BDJ_TYPE):java-build-support
diff --git a/configure.ac b/configure.ac
index c7016344..d654a5a8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -131,6 +131,10 @@ AC_ARG_WITH([bdj-bootclasspath],
 
 AC_ARG_WITH([java9],
   [AS_HELP_STRING([--with-java9], [build with Java 9+ (drop support for Java <1.6) @<:@default=without@:>@])])
+AC_ARG_WITH([java12],
+  [AS_HELP_STRING([--with-java9], [build with Java 12+ (drop support for Java <1.7) @<:@default=without@:>@])])
+AC_ARG_WITH([java20],
+  [AS_HELP_STRING([--with-java20], [build with Java 20+ (drop support for Java <1.8) @<:@default=without@:>@])])
 
 AC_ARG_WITH([external-libudfread],
   [AS_HELP_STRING([--without-external-libudfread],
@@ -293,10 +297,12 @@ AS_IF([test "x$use_bdjava_jar" = "xyes"], [
         javac_version=`"$JAVAC" -version 2>&1 | head -n 1`
         [with_java9=`echo "$javac_version" | grep -E -q '^javac\ (9|1[0-1])' && echo yes`]
         [with_java12=`echo "$javac_version" | grep -E -q '^javac\ (1[2-9])' && echo yes`]
+        [with_java20=`echo "$javac_version" | grep -E -q '^javac\ ([2-9][0-9])' && echo yes`]
     ])
 
     AS_IF([test "x$with_java9" = "xyes" -a "$BDJ_TYPE" != "j2me"], [java_code_version=1.6], [java_code_version=1.4])
     AS_IF([test "x$with_java12" = "xyes" -a "$BDJ_TYPE" != "j2me"], [java_code_version=1.7])
+    AS_IF([test "x$with_java20" = "xyes" -a "$BDJ_TYPE" != "j2me"], [java_code_version=1.8])
 ])
 
 AC_DEFINE_UNQUOTED([JAVA_ARCH], ["$java_arch"], ["Defines the architecture of the java vm."])
@@ -304,6 +310,7 @@ AC_DEFINE_UNQUOTED([JDK_HOME], ["$JDK_HOME"], [""])
 AM_CONDITIONAL([USING_BDJAVA_BUILD_JAR], [ test $use_bdjava_jar = "yes" ])
 AM_CONDITIONAL([USING_JAVAC_9], [ test x"$with_java9" = x"yes" ])
 AM_CONDITIONAL([USING_JAVAC_12], [ test x"$with_java12" = x"yes" ])
+AM_CONDITIONAL([USING_JAVAC_20], [ test x"$with_java20" = x"yes" ])
 
 dnl BD-J type
 if test "$BDJ_TYPE" = "j2me"; then