[gn build] (manually) port 4a16fe13 (debuginfod)

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

+static_library("Debuginfod") {
+  output_name = "LLVMDebuginfod"
+  deps = [ "//llvm/lib/Support" ]
+  sources = [ "Debuginfod.cpp" ]
+}

llvm/utils/gn/secondary/llvm/unittests/BUILD.gn

@@ -15,6 +15,7 @@ group("unittests") {
     "DebugInfo/GSYM:DebugInfoGSYMTests",
     "DebugInfo/MSF:DebugInfoMSFTests",
     "DebugInfo/PDB:DebugInfoPDBTests",
+    "Debuginfod:DebuginfodTests",
     "Demangle:DemangleTests",
     "ExecutionEngine:ExecutionEngineTests",
     "ExecutionEngine/JITLink:JITLinkTests",

llvm/utils/gn/secondary/llvm/unittests/Debuginfod/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("DebuginfodTests") {
+  deps = [
+    "//llvm/lib/Debuginfod",
+    "//llvm/lib/Testing/Support",
+  ]
+  sources = [ "DebuginfodTests.cpp" ]
+}