gn build: Unbreak Windows build

[thakis]

Summary

I didn't break all that much during upstreaming, just needs two small fixes:

• fix spelling of MCJITTests.def file
• make libLTO a shared_library to put it in bin/ on Windows where it is in the CMake build too

[phosek]

LGTM

llvm/utils/gn/secondary/llvm/tools/lto/BUILD.gn

 import("//llvm/version.gni")
 
-lto_target_type = "loadable_module"
+lto_target_type = "shared_library"
 if (host_os == "linux") {
   # Linux needs -fPIC to build shared libs but they aren't on by default.
   # For now, make libclang a static lib there.
   lto_target_type = "static_library"
 }
 
 target(lto_target_type, "lto") {
-  output_name = "libLTO"
+  output_name = "LTO"
   deps = [
     "//llvm/lib/Bitcode/Reader",
     "//llvm/lib/IR",
     "//llvm/lib/LTO",
     "//llvm/lib/MC",
     "//llvm/lib/MC/MCDisassembler",
     "//llvm/lib/Support",
     "//llvm/lib/Target",

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

sources = [
     "MCJITCAPITest.cpp",
     "MCJITMemoryManagerTest.cpp",
     "MCJITMultipleModuleTest.cpp",
     "MCJITObjectCacheTest.cpp",
     "MCJITTest.cpp",
   ]
 
   if (host_os == "win") {
-    sources += [ "MCJITTest.def" ]
+    sources += [ "MCJITTests.def" ]
   }
 }