configure: detect redundant --with-libpcre & --with-libpcre1

The --with-libpcre option is a synonym for the --with-libpcre1 flag,
but the configure script allowed for redundantly specifying both.

Nothing broke as a result of this, but it's confusing, so let's
disallow it.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

configure.ac

@@ -280,6 +280,10 @@ AS_HELP_STRING([--with-libpcre],[synonym for --with-libpcre1]),
 AC_ARG_WITH(libpcre1,
 AS_HELP_STRING([--with-libpcre1],[support Perl-compatible regexes via libpcre1 (default is NO)])
 AS_HELP_STRING([],           [ARG can be also prefix for libpcre library and headers]),
+    if test -n "$USE_LIBPCRE1"; then
+        AC_MSG_ERROR([Only supply one of --with-libpcre or its synonym --with-libpcre1!])
+    fi
+
     if test "$withval" = "no"; then
 	USE_LIBPCRE1=
     elif test "$withval" = "yes"; then