Refactor the mpir/spkg-configure.m4 (and to a lesser extent the one f…

…or gmp) to use the new pre and post arguments to SAGE_SPKG_CONFIGURE

This allows us to ensure that certain actions (such as providing a default
value for SAGE_MP_LIBRARY) are always performed by the configure script even if
the SPKG will not otherwise be installed for some reason (e.g. due to skipping
a configure check).

build/pkgs/mpir/spkg-configure.m4

@@ -1,22 +1,4 @@
 SAGE_SPKG_CONFIGURE([mpir], [
-    AC_ARG_WITH([mp],
-    [AS_HELP_STRING([--with-mp=system],
-        [use the system GMP as multiprecision library, if possible (default)])]
-    [AS_HELP_STRING([--with-mp=mpir],
-        [use the Sage SPKG for MPIR as multiprecision library])]
-    [AS_HELP_STRING([--with-mp=gmp],
-        [use the Sage SPKG for GMP as multiprecision library])])
-
-dnl Just part the options here
-    case "$with_mp" in
-        system) ;;
-        MPIR|mpir) with_mp=mpir;;
-        GMP|gmp) with_mp=gmp;;
-        "") with_mp=system;;
-        *)
-            AC_MSG_ERROR([allowed values for --with-mp are system, mpir, or gmp]);;
-    esac
-
 dnl Implement cases for what to do on different options here
     case "$with_mp" in
         system)
@@ -36,7 +18,37 @@ dnl Implement cases for what to do on different options here
             SAGE_MP_LIBRARY=gmp
             ;;
     esac
+], [], [
+    AC_ARG_WITH([mp],
+    [AS_HELP_STRING([--with-mp=system],
+        [use the system GMP as multiprecision library, if possible (default)])]
+    [AS_HELP_STRING([--with-mp=mpir],
+        [use the Sage SPKG for MPIR as multiprecision library])]
+    [AS_HELP_STRING([--with-mp=gmp],
+        [use the Sage SPKG for GMP as multiprecision library])])
 
+dnl Just parse the options here
+    case "$with_mp" in
+        system) ;;
+        MPIR|mpir) with_mp=mpir;;
+        GMP|gmp) with_mp=gmp;;
+        "") with_mp=system;;
+        *)
+            AC_MSG_ERROR([allowed values for --with-mp are system, mpir, or gmp]);;
+    esac
+
+dnl Set SAGE_MP_LIBRARY depending on the with_mp option
+    case "$with_mp" in
+    mpir|system)
+        SAGE_MP_LIBRARY=mpir
+        ;;
+    gmp)
+        SAGE_MP_LIBRARY=gmp
+        ;;
+    esac
+
+    AC_SUBST([SAGE_MP_LIBRARY], [$SAGE_MP_LIBRARY])
+], [
     if test x$sage_spkg_install_mpir = xyes -o x$sage_spkg_install_gmp = xyes; then
         AC_SUBST(SAGE_GMP_PREFIX, ['$SAGE_LOCAL'])
         AC_SUBST(SAGE_GMP_INCLUDE, ['$SAGE_LOCAL/include'])
@@ -56,7 +68,5 @@ dnl Implement cases for what to do on different options here
         AC_SUBST(SAGE_GMP_PREFIX, [''])
         AC_MSG_RESULT([using GMP-compatible library from the system])
     fi
-
-    AC_SUBST([SAGE_MP_LIBRARY], [$SAGE_MP_LIBRARY])
 ])