Make --without-gmp/--with-gmp=no work.

[[Imported from SVN: r5920]]

m4/gmp.m4

@@ -22,33 +22,38 @@
 AC_DEFUN([DUNE_PATH_GMP],[
   AC_REQUIRE([AC_PROG_CXX])
 
-  AC_ARG_WITH(gmp,
-    AS_HELP_STRING([--with-gmp=PATH],
-                   [directory to GMP (GNU MP Bignum Library)]))
-  AS_IF([test x$with_gmp = x],[with_gmp=/usr])
+  AC_ARG_WITH([gmp],
+    [AS_HELP_STRING([--with-gmp=PATH],
+                   [directory to GMP (GNU MP Bignum Library)])],
+    [],
+    [with_gmp=/usr])
 
   HAVE_GMP=no
-  GMP_CPPFLAGS="-I$with_gmp/include -DENABLE_GMP=1"
-  GMP_LIBS="-L$with_gmp/lib -lgmpxx -lgmp"
+  AS_IF([test x"$with_gmp" = x"no"], [
+    AC_MSG_NOTICE([skipping check for GMP])
+  ], [
+    GMP_CPPFLAGS="-I$with_gmp/include -DENABLE_GMP=1"
+    GMP_LIBS="-L$with_gmp/lib -lgmpxx -lgmp"
 
-  AC_LANG_PUSH([C++])
-  ac_save_CPPFLAGS="$CPPFLAGS"
-  ac_save_LIBS="$LIBS"
+    AC_LANG_PUSH([C++])
+    ac_save_CPPFLAGS="$CPPFLAGS"
+    ac_save_LIBS="$LIBS"
 
-  CPPFLAGS="$CPPFLAGS $GMP_CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $GMP_CPPFLAGS"
 
-  AC_CHECK_HEADER([gmpxx.h], [HAVE_GMP=yes],
-    AC_MSG_WARN([gmpxx.h not found in $with_gmp]))
+    AC_CHECK_HEADER([gmpxx.h], [HAVE_GMP=yes],
+      [AC_MSG_WARN([gmpxx.h not found in $with_gmp])])
 
-  AS_IF([test $HAVE_GMP = yes],[
-    DUNE_CHECK_LIB_EXT([$with_gmp/lib], gmp,[__gmpz_abs],[],[
-      HAVE_GMP=no
-      AC_MSG_WARN(libgmp not found)])
-  ])
+    AS_IF([test $HAVE_GMP = yes],[
+      DUNE_CHECK_LIB_EXT([$with_gmp/lib], gmp,[__gmpz_abs],[],[
+        HAVE_GMP=no
+        AC_MSG_WARN(libgmp not found)])
+    ])
 
-  CPPFLAGS="$ac_save_CPPFLAGS"
-  LIBS="$ac_save_LIBS"
-  AC_LANG_POP([C++])
+    CPPFLAGS="$ac_save_CPPFLAGS"
+    LIBS="$ac_save_LIBS"
+    AC_LANG_POP([C++])
+  ])
 
   AS_IF([test $HAVE_GMP = yes],[
     AC_DEFINE([HAVE_GMP],[ENABLE_GMP],[Was GMP found and GMP_CPPFLAGS used?])