configure: allow user to specify what gdb to use

This is useful, especially when testing relatively new gdbstub
features that might not be in distro packages yet.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200316172155.971-22-alex.bennee@linaro.org>

configure

@@ -303,6 +303,7 @@ libs_qga=""
 debug_info="yes"
 stack_protector=""
 use_containers="yes"
+gdb_bin=$(command -v "gdb")
 
 if test -e "$source_path/.git"
 then
@@ -1588,6 +1589,8 @@ for opt do
   ;;
   --disable-fuzzing) fuzzing=no
   ;;
+  --gdb=*) gdb_bin="$optarg"
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1773,6 +1776,7 @@ Advanced options (experts only):
   --enable-plugins
                            enable plugins via shared library loading
   --disable-containers     don't use containers for cross-building
+  --gdb=GDB-path           gdb to use for gdbstub tests [$gdb_bin]
 
 Optional features, enabled with --enable-FEATURE and
 disabled with --disable-FEATURE, default is enabled if available:
@@ -6734,6 +6738,7 @@ echo "libudev           $libudev"
 echo "default devices   $default_devices"
 echo "plugin support    $plugins"
 echo "fuzzing support   $fuzzing"
+echo "gdb               $gdb_bin"
 
 if test "$supported_cpu" = "no"; then
     echo
@@ -7608,6 +7613,10 @@ if test "$plugins" = "yes" ; then
     fi
 fi
 
+if test -n "$gdb_bin" ; then
+    echo "HAVE_GDB_BIN=$gdb_bin" >> $config_host_mak
+fi
+
 if test "$tcg_interpreter" = "yes"; then
   QEMU_INCLUDES="-iquote \$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
 elif test "$ARCH" = "sparc64" ; then