[configure] accept clang/llvm 11

configure.ac

@@ -62,9 +62,9 @@ AC_SUBST(RUN_TESTS)
 DEFAULT_FC_C_HEADERS=$datarootdir/frama-c/libc
 DEFAULT_FC_CXX_HEADERS=$datarootdir/libc++
 
-AC_CHECK_PROGS([CLANG],[clang clang-10 clang-9 clang-8 clang-7 clang-6.0],no)
-AC_CHECK_PROGS([CLANGXX],[clang++ clang++-10 clang++-9 clang++-8 clang++-7 clang++6.0],no)
-AC_CHECK_PROGS([LLVM_CONFIG],[llvm-config llvm-config-10 llvm-config-9 llvm-config-8 llvm-config-7 llvm-config-6.0],no)
+AC_CHECK_PROGS([CLANG],[clang clang-11 clang-10 clang-9 clang-8 clang-7 clang-6.0],no)
+AC_CHECK_PROGS([CLANGXX],[clang++ clang++-11 clang++-10 clang++-9 clang++-8 clang++-7 clang++6.0],no)
+AC_CHECK_PROGS([LLVM_CONFIG],[llvm-config llvm-config-11 llvm-config-10 llvm-config-9 llvm-config-8 llvm-config-7 llvm-config-6.0],no)
 
 if test "$LLVM_CONFIG" = "no"; then
   plugin_disable(frama_clang,[llvm-config not found]);
@@ -92,6 +92,7 @@ case $LLVM_VERSION in
   8.0.*) AC_MSG_RESULT([$LLVM_VERSION: Good]);;
   9.0.*) AC_MSG_RESULT([$LLVM_VERSION: Good]); RUN_TESTS=yes;;
   10.0.*) AC_MSG_RESULT([$LLVM_VERSION: Good]); RUN_TESTS=yes;;
+  11.0.*) AC_MSG_RESULT([$LLVM_VERSION: Good]); RUN_TESTS=yes;;
   *) plugin_disable(frama_clang,
       [[LLVM Version $LLVM_VERSION is not supported. Please install LLVM 6.0.x, 7.0.x, 8.0.x, 9.0.x, or 10.0.x]]);;
 esac