Change @ -> % in config files. @name@ might be needed for config files to

Change @ -> % in config files. @name@ might be needed for config files to
themselves be configured via autoconf so its not a good substitition syntax
for llvmc. Furthermore % is more llvmish :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15957 91177308-0d34-0410-b5e6-96231b3b80d8