Configure: check for GCC 6 and 7

diff --git a/Configure b/Configure
index 3259249..bdcfaf1 100755 (executable)
--- a/Configure
+++ b/Configure
@@ -23612,7 +23612,7 @@ fi
 
 : add -D_FORTIFY_SOURCE if feasible and not already there
 case "$gccversion" in
-[45].*)        case "$optimize$ccflags" in
+[4567].*)      case "$optimize$ccflags" in
        *-O*)   case "$ccflags$cppsymbols" in
                *_FORTIFY_SOURCE=*) # Don't add it again.
                        echo "You seem to have -D_FORTIFY_SOURCE already, not adding it." >&4