Refactor RyuJIT/x86 long decomposition code

All decomposition code is now in decompose.cpp, in a Decompose class.
Each node type that is decomposed has its own member function to do
the decomposition. Various helpers have been added to reduce code
duplication. In general, though, the code is as it was before.

Author: BruceForstall

src/jit/CMakeLists.txt

@@ -84,6 +84,7 @@ if(CLR_CMAKE_TARGET_ARCH_AMD64)
 elseif(CLR_CMAKE_TARGET_ARCH_ARM)
   set( ARCH_SOURCES
     codegenarm.cpp
+    decomposelongs.cpp
     emitarm.cpp
     lowerarm.cpp
     targetarm.cpp
@@ -92,6 +93,7 @@ elseif(CLR_CMAKE_TARGET_ARCH_ARM)
 elseif(CLR_CMAKE_TARGET_ARCH_I386)
   set( ARCH_SOURCES
     codegenxarch.cpp
+    decomposelongs.cpp
     emitxarch.cpp
     lowerxarch.cpp
     simd.cpp

src/jit/compiler.h

@@ -1385,6 +1385,10 @@ class   Compiler
     friend class LclVarDsc;
     friend class TempDsc;
 
+#ifndef _TARGET_64BIT_
+    friend class DecomposeLongs;
+#endif // !_TARGET_64BIT_
+
 /*
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