I've NMU'ed these bugs, uploaded to DELAYED-5days.
diff -Nru mlton-20100608/debian/changelog mlton-20100608/debian/changelog
--- mlton-20100608/debian/changelog 2011-07-19 12:37:02.000000000 +0200
+++ mlton-20100608/debian/changelog 2013-10-19 19:45:37.000000000 +0200
@@ -1,3 +1,13 @@
+mlton (20100608-5.1) unstable; urgency=low
+
+ * Non-Maintainer Upload
+ * Apply upstream patch to avoid __gmp_const breakage
+ (Closes: 707410)
+ * Apply patch from Matthias Klose to allow building on more target
+ triplets on i386, not just i486-linux-gnu (Closes: 640137)
+
+ -- Florian Weimer <f...@deneb.enyo.de> Sat, 19 Oct 2013 19:39:58 +0200
+
mlton (20100608-5) unstable; urgency=low
* Newest gcc and binutils fix mips[el] jump problem
diff -Nru mlton-20100608/debian/mlton-runtime-i486-linux-gnu.install
mlton-20100608/debian/mlton-runtime-i486-linux-gnu.install
--- mlton-20100608/debian/mlton-runtime-i486-linux-gnu.install 2011-03-21
19:55:23.000000000 +0100
+++ mlton-20100608/debian/mlton-runtime-i486-linux-gnu.install 2013-10-19
19:44:39.000000000 +0200
@@ -1 +1 @@
-usr/lib/mlton/targets/i486-linux-gnu/*
+usr/lib/mlton/targets/i*86-linux-gnu/*
diff -Nru mlton-20100608/debian/patches/Replace-__gmp_const-with-const.patch
mlton-20100608/debian/patches/Replace-__gmp_const-with-const.patch
--- mlton-20100608/debian/patches/Replace-__gmp_const-with-const.patch
1970-01-01 01:00:00.000000000 +0100
+++ mlton-20100608/debian/patches/Replace-__gmp_const-with-const.patch
2013-10-19 19:36:53.000000000 +0200
@@ -0,0 +1,55 @@
+From a658a1f4a76a01f568116598800f49b80cf8ee1a Mon Sep 17 00:00:00 2001
+From: David Larsen <dcl9...@cs.rit.edu>
+Date: Wed, 17 Apr 2013 15:28:24 -0400
+Subject: [PATCH] Replace '__gmp_const' with 'const'
+
+The __gmp_const macro was added to GMP as a workaround for C compilers
+which didn't support the const keyword. GMP 5.1 removed support for
+pre-ANSI C compilers, so the __gmp_const workaround was removed at the
+same time.
+
+This change replaces all uses of '__gmp_const' with uses of the 'const'
+keword directly, since MLton already expects C99 support from the system
+C compiler.
+
+This should fix the build errors for systems using GMP >= 5.1.
+---
+ runtime/gc/int-inf.c | 8 ++++----
+ 1 file changed, 4 insertions(+), 4 deletions(-)
+
+diff --git a/runtime/gc/int-inf.c b/runtime/gc/int-inf.c
+index 7f24e64..6a91390 100644
+--- a/runtime/gc/int-inf.c
++++ b/runtime/gc/int-inf.c
+@@ -181,8 +181,8 @@ objptr finiIntInfRes (GC_state s, __mpz_struct *res,
size_t bytes) {
+
+ static inline objptr binary (objptr lhs, objptr rhs, size_t bytes,
+ void(*binop)(__mpz_struct *resmpz,
+- __gmp_const __mpz_struct *lhsspace,
+- __gmp_const __mpz_struct
*rhsspace)) {
++ const __mpz_struct *lhsspace,
++ const __mpz_struct *rhsspace)) {
+ __mpz_struct lhsmpz, rhsmpz, resmpz;
+ mp_limb_t lhsspace[LIMBS_PER_OBJPTR + 1], rhsspace[LIMBS_PER_OBJPTR + 1];
+
+@@ -258,7 +258,7 @@ objptr IntInf_xorb (objptr lhs, objptr rhs, size_t bytes) {
+
+ static objptr unary (objptr arg, size_t bytes,
+ void(*unop)(__mpz_struct *resmpz,
+- __gmp_const __mpz_struct *argspace)) {
++ const __mpz_struct *argspace)) {
+ __mpz_struct argmpz, resmpz;
+ mp_limb_t argspace[LIMBS_PER_OBJPTR + 1];
+
+@@ -284,7 +284,7 @@ objptr IntInf_notb (objptr arg, size_t bytes) {
+
+ static objptr shary (objptr arg, Word32_t shift, size_t bytes,
+ void(*shop)(__mpz_struct *resmpz,
+- __gmp_const __mpz_struct *argspace,
++ const __mpz_struct *argspace,
+ unsigned long shift))
+ {
+ __mpz_struct argmpz, resmpz;
+--
+1.7.10.4
+
diff -Nru mlton-20100608/debian/patches/series
mlton-20100608/debian/patches/series
--- mlton-20100608/debian/patches/series 2011-07-19 13:54:28.000000000
+0200
+++ mlton-20100608/debian/patches/series 2013-10-19 19:37:48.000000000
+0200
@@ -1,2 +1,3 @@
11-fixes-20100608-to-20110319.patch
22-fixes-20110319-to-20110719.patch
+Replace-__gmp_const-with-const.patch
--
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