[WebAssembly] Create a TargetInfo header.  NFC

Move the declarations of getThe<Name>Target() functions into a new header in
TargetInfo and make users of these functions include this new header.
This fixes a layering problem.

llvm-svn: 360735
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index 22033fe..565438d 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -17,6 +17,7 @@
 #include "MCTargetDesc/WebAssemblyInstPrinter.h"
 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
+#include "TargetInfo/WebAssemblyTargetInfo.h"
 #include "WebAssembly.h"
 #include "WebAssemblyMCInstLower.h"
 #include "WebAssemblyMachineFunctionInfo.h"