[CodeGen/DWARF] Introduce DWARF tag for SwiftTail and emit it in CodeGen.

swifttailcc is a new calling convention in LLVM introduced in
https://reviews.llvm.org/D95443. We add a new DWARF tag to capture
this in debuginfo.

Differential Revision: https://reviews.llvm.org/D95704

[Note: This patch seems to have been forgotten about, landing it now with considerable delay]

(cherry picked from commit 380f0fb)

 Conflicts:
	llvm/include/llvm/BinaryFormat/Dwarf.def

WARNING. This patch was put up for LLVM review and then forgotten
about. In the mean time the DW_CC constant was used by another LLVM
extension. So this patch actually changes the debug info
format. Thankfully, there don't seem to be any consumers depending on
the information right now, so this should be benign.

Author: adrian-prantl

llvm/include/llvm/BinaryFormat/Dwarf.def

@@ -1042,7 +1042,10 @@ HANDLE_DW_CC(0xc8, LLVM_Swift)
 HANDLE_DW_CC(0xc9, LLVM_PreserveMost)
 HANDLE_DW_CC(0xca, LLVM_PreserveAll)
 HANDLE_DW_CC(0xcb, LLVM_X86RegCall)
-HANDLE_DW_CC(0xcc, LLVM_SwiftTail)
+HANDLE_DW_CC(0xcc, LLVM_M68kRTD)
+HANDLE_DW_CC(0xcd, LLVM_PreserveNone)
+HANDLE_DW_CC(0xce, LLVM_RISCVVectorCall)
+HANDLE_DW_CC(0xcf, LLVM_SwiftTail)
 // From GCC source code (include/dwarf2.h): This DW_CC_ value is not currently
 // generated by any toolchain.  It is used internally to GDB to indicate OpenCL
 // C functions that have been compiled with the IBM XL C for OpenCL compiler and