Specify "build" but not "host" for gmp and mpfr

The "--host" flag to configure defaults to "--build", and explicitly
passing it is normally reserved for cross-compiling.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/gmp.rb

@@ -27,7 +27,7 @@ class Gmp < Formula
       args << "--build=x86_64-apple-darwin"
     else
       ENV.m32
-      args << "--host=none-apple-darwin"
+      args << "--build=none-apple-darwin"
     end
 
     system "./configure", *args

Formula/mpfr.rb

@@ -25,7 +25,7 @@ class Mpfr < Formula
       args << "--build=x86_64-apple-darwin"
     else
       ENV.m32
-      args << "--host=none-apple-darwin"
+      args << "--build=none-apple-darwin"
     end
 
     system "./configure", *args