Fix libgmp.dylib's identity.

  * gmp.h: libgmp.dylib's identity, as built, is $prefix/lib/libgmp.10.dylib.
      Because of a misunderstanding about iains's changes to runpath
      handling, I'd changed this to @rpath/libgmp.10.dylib.
      Reverted.

gmp.sh

@@ -9,21 +9,11 @@ rm -rf *
 $GCC_SRC/gmp/configure                          \
   --prefix=$PREFIX                              \
   --host=$BUILD                                 \
+  --target=$BUILD                               \
+  --build=$BUILD                                \
   --enable-cxx                                  \
   --enable-shared
 
 make -w -j7
 
-# Can't find a way to make the shared library identities to start
-# @rpath, so fix up.
-(
-    set -eu
-    cd .libs
-    for lib in $(find . -type f -name \*.dylib); do
-        # remove the leading "./"
-        l=$(echo $lib | cut -b3-)
-        install_name_tool -id @rpath/$l $lib
-    done
-)
-
 make install