[CMake] Add configuration dirs as potential locations for llvm-lit and llvm-tblgen in standalone builds
[CMake] Add configuration dirs as potential locations for llvm-lit and llvm-tblgen in standalone builds

Summary:
If the provided LLVM build-tree used a multi-configuration generator like Xcode, `LLVM_TOOLS_BINARY_DIR` will have a generator-specific placeholder to express `CMAKE_CFG_INTDIR`. Thus `llvm-lit` and `llvm-tblgen` won't be found.
D62878 exports the actual configuration types so we can fix the path and add them to the search paths for `find_program()`.

Reviewers: xiaobai, labath, stella.stamenova

Reviewed By: xiaobai, stella.stamenova

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D62879

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@362589 91177308-0d34-0410-b5e6-96231b3b80d8

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