[PECOFF] Ignore /functionpadmin option.

If /functionpadmin is specified, the linker is supposed to make room at the
beginning of each function, so that self-modifying program would easily
hotpatch existing functions. Since I'm not sure if this feature is really used,
I'll make LLD to ignore the option for now.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@196363 91177308-0d34-0410-b5e6-96231b3b80d8