[COFF, ARM64] Emit COFF function header

Summary:
Emit COFF header when printing out the function. This is important as the
header contains two important pieces of information: the storage class for the
symbol and the symbol type information. This bit of information is required for
the linker to correctly identify the type of symbol that it is dealing with.

This patch mimics X86 and ARM COFF behavior for function header emission.

Reviewers: rnk, mstorsjo, compnerd, TomTan, ssijaric

Reviewed By: mstorsjo

Subscribers: dmajor, javed.absar, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D55535

llvm-svn: 348875