[Support/ELF] Add OpenBSD PT_OPENBSD_SYSCALLS constant.

Reference: https://github.com/openbsd/src/blob/master/sys/sys/exec_elf.h
(cherry picked from commit 97eff26)

Author: fcambus

llvm/include/llvm/BinaryFormat/ELF.h

@@ -1464,6 +1464,7 @@ enum {
   PT_OPENBSD_RANDOMIZE = 0x65a3dbe6, // Fill with random data.
   PT_OPENBSD_WXNEEDED = 0x65a3dbe7,  // Program does W^X violations.
   PT_OPENBSD_NOBTCFI = 0x65a3dbe8,   // Do not enforce branch target CFI.
+  PT_OPENBSD_SYSCALLS = 0x65a3dbe9,  // System call sites.
   PT_OPENBSD_BOOTDATA = 0x65a41be6,  // Section for boot arguments.
 
   // ARM program header types.