Fix various macos issues.

scripts/common.m4

@@ -13,7 +13,7 @@ AC_DEFUN([TORRENT_WITH_SYSROOT], [
         AC_MSG_ERROR(The sysroot option must point to a directory, like f.ex "/Developer/SDKs/MacOSX10.4u.sdk".)
       else
         AC_MSG_RESULT($withval)
-        
+
         CXXFLAGS="$CXXFLAGS -isysroot $withval"
         LDFLAGS="$LDFLAGS -Wl,-syslibroot,$withval"
       fi
@@ -21,6 +21,19 @@ AC_DEFUN([TORRENT_WITH_SYSROOT], [
 ])
 
 
+AC_DEFUN([TORRENT_REMOVE_UNWANTED],
+[
+  values_to_check=`for i in $2; do echo $i; done`
+  unwanted_values=`for i in $3; do echo $i; done`
+  if test -z "${unwanted_values}"; then
+    $1="$2"
+  else
+    result=`echo "${values_to_check}" | $GREP -Fvx -- "${unwanted_values}" | $GREP -v '^$'`
+    $1=${result//$'\n'/ }
+  fi
+])
+
+
 AC_DEFUN([TORRENT_ENABLE_ARCH], [
   AC_ARG_ENABLE(arch,
     AS_HELP_STRING([--enable-arch=ARCH],