configure: Fix arch detection for GDB_HAS_MTE

GDB_HAS_MTE must only be set if GDB supports the aarch64 arch, so the
test if "aarch64" string is present must be against GDB-related
'$gdb_arches' variable and not against '$arch' variable.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-Id: <20240804161850.2646299-2-gustavo.romero@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240813202329.1237572-4-alex.bennee@linaro.org>

configure

@@ -1673,7 +1673,7 @@ for target in $target_list; do
           echo "GDB=$gdb_bin" >> $config_target_mak
       fi
 
-      if test "${arch}" = "aarch64" && version_ge ${gdb_version##* } 15.0; then
+      if test "${gdb_arches#*aarch64}" != "$gdb_arches" && version_ge ${gdb_version##* } 15.0; then
           echo "GDB_HAS_MTE=y" >> $config_target_mak
       fi