Merge pull request #40 from jeremy/with-gcc-flag

set --with-gcc=gcc-4.2 on lion + xcode 4.1

bin/ruby-build

@@ -151,6 +151,7 @@ use_gcc42_on_lion() {
   if [ "$(uname -s)" = "Darwin" ]; then
     if [ "$(expr "$(sw_vers -productVersion | cut -f 2 -d .)" \>= 7 || true)" -eq 1 ]; then
       export CC=/usr/bin/gcc-4.2
+      CONFIGURE_OPTS="--with-gcc=$CC $CONFIGURE_OPTS"
     fi
   fi
 }