[gn build] Port 911a6f2

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/source/Plugins/Process/elf-core/BUILD.gn

@@ -18,6 +18,7 @@ static_library("elf-core") {
     "RegisterContextLinuxCore_x86_64.cpp",
     "RegisterContextPOSIXCore_arm.cpp",
     "RegisterContextPOSIXCore_arm64.cpp",
+    "RegisterContextPOSIXCore_loongarch64.cpp",
     "RegisterContextPOSIXCore_mips64.cpp",
     "RegisterContextPOSIXCore_powerpc.cpp",
     "RegisterContextPOSIXCore_ppc64le.cpp",