Note how to build with Clang. (gcc gave lots of warnings on

my Linux machine.)

README.md

@@ -63,7 +63,7 @@ Building and Running Translation Validation
 
 Alive2's `opt` and `clang` translation validation requires a build of LLVM with
 RTTI and exceptions turned on.
-LLVM can be built targeting X86 in the following way:
+LLVM can be built targeting X86 in the following way.  (You may prefer to add `-DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++` to the CMake step if your default compiler is `gcc`.)
 ```
 cd $LLVM2_HOME
 mkdir build