Optionally, Clang now builds using LLVM as an external library.
Optionally, Clang now builds using LLVM as an external library.

The user sets the variable CLANG_PATH_TO_LLVM_BUILD pointing to a LLVM
build directory or to a directory where LLVM was installed. When using
a non-installed LLVM build, it is necessary to set
CLANG_PATH_TO_LLVM_SOURCE as well.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@124817 91177308-0d34-0410-b5e6-96231b3b80d8

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