[COFF, ARM64] Add support for Windows ARM64 COFF format

Summary:
This is the llvm part of the initial implementation to support Windows ARM64 COFF format.
I will gradually add more functionality in subsequent patches.

Reviewers: ruiu, rnk, t.p.northover, compnerd

Reviewed By: ruiu, compnerd

Subscribers: aemerson, mgorny, javed.absar, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D34705

llvm-svn: 306490
diff --git a/llvm/test/MC/AArch64/coff-basic.ll b/llvm/test/MC/AArch64/coff-basic.ll
new file mode 100644
index 0000000..23f06b5
--- /dev/null
+++ b/llvm/test/MC/AArch64/coff-basic.ll
@@ -0,0 +1,8 @@
+; RUN: llc -mtriple aarch64-windows < %s | FileCheck %s
+
+define i32 @foo() {
+entry:
+  ret i32 1
+}
+
+; CHECK: .globl foo