This is a gross hack to cross build libgnatprj without having the
gmp.h header for the target architecture.  Are libgnatvsn and libgnatprj
really target libraries, or host libraries? The odd thing is that
the gnat cross build tools are not linked against these two libraries.

Index: b/src/gcc/wide-int.h
===================================================================
--- a/src/gcc/wide-int.h
+++ b/src/gcc/wide-int.h
@@ -3106,8 +3106,10 @@ namespace wi
   wide_int from_buffer (const unsigned char *, unsigned int);
 
 #ifndef GENERATOR_FILE
+#ifndef LIBGNATPRJ_CROSS_HACK
   void to_mpz (const wide_int_ref &, mpz_t, signop);
 #endif
+#endif
 
   wide_int mask (unsigned int, bool, unsigned int);
   wide_int shifted_mask (unsigned int, unsigned int, bool, unsigned int);
Index: b/src/gcc/system.h
===================================================================
--- a/src/gcc/system.h
+++ b/src/gcc/system.h
@@ -678,8 +678,10 @@ extern int vsnprintf (char *, size_t, co
 
 /* Do not introduce a gmp.h dependency on the build system.  */
 #ifndef GENERATOR_FILE
+#ifndef LIBGNATPRJ_CROSS_HACK
 #include <gmp.h>
 #endif
+#endif
 
 /* Get libiberty declarations.  */
 #include "libiberty.h"
Index: b/src/libgnatprj/Makefile.in
===================================================================
--- a/src/libgnatprj/Makefile.in
+++ b/src/libgnatprj/Makefile.in
@@ -37,7 +37,7 @@ TOOLS_TARGET_PAIRS := @TOOLS_TARGET_PAIR
 LN_S := @LN_S@
 
 ifneq (@build@,@host@)
-   CFLAGS += -b @host@
+   override CFLAGS += -DLIBGNATPRJ_CROSS_HACK
 endif
 
 .PHONY: libgnatprj install
Index: b/src/gcc/double-int.h
===================================================================
--- a/src/gcc/double-int.h
+++ b/src/gcc/double-int.h
@@ -429,11 +429,13 @@ double_int::popcount () const
 
 
 #ifndef GENERATOR_FILE
+#ifndef LIBGNATPRJ_CROSS_HACK
 /* Conversion to and from GMP integer representations.  */
 
 void mpz_set_double_int (mpz_t, double_int, bool);
 double_int mpz_get_double_int (const_tree, mpz_t, bool);
 #endif
+#endif
 
 namespace wi
 {