[gn build] Port 9b41b62

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/MC/BUILD.gn

@@ -57,12 +57,7 @@ static_library("MC") {
     "MCSPIRVStreamer.cpp",
     "MCSchedule.cpp",
     "MCSection.cpp",
-    "MCSectionCOFF.cpp",
-    "MCSectionELF.cpp",
-    "MCSectionGOFF.cpp",
     "MCSectionMachO.cpp",
-    "MCSectionWasm.cpp",
-    "MCSectionXCOFF.cpp",
     "MCStreamer.cpp",
     "MCSubtargetInfo.cpp",
     "MCSymbol.cpp",