[gn build] Port 096ab51

Author: llvmgnsyncbot

llvm/utils/gn/secondary/lldb/source/Plugins/Process/Utility/BUILD.gn

@@ -39,6 +39,7 @@ static_library("Utility") {
     "RegisterContextDarwin_arm.cpp",
     "RegisterContextDarwin_arm64.cpp",
     "RegisterContextDarwin_i386.cpp",
+    "RegisterContextDarwin_riscv32.cpp",
     "RegisterContextDarwin_x86_64.cpp",
     "RegisterContextDummy.cpp",
     "RegisterContextFreeBSD_i386.cpp",