The new option makes it possible to build external projects as part of
the llvm build without copying (or symlinking) then into llvm/tool with
specifying a few additional cmake variables.
Example usage (2 additional project called foo and bar):
-DLLVM_EXTERNAL_PROJECTS="Foo;Bar"
-DLLVM_EXTERNAL_FOO_SOURCE_DIR=/src/foo
-DLLVM_EXTERNAL_BAR_SOURCE_DIR=/src/bar
Note: This is the extension of the approach we already support for
clang/lldb/poly with adding an option to specify additional supported
projects.
Differential revision: http://reviews.llvm.org/D20838
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271440 91177308-0d34-0410-b5e6-96231b3b80d8
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