Without this patch, the clang Analysis plugin examples (in clang/lib/Analysis/plugins) are always built and installed even if CLANG_BUILD_EXAMPLES is OFF.
When using llvm-toolchain-bionic in http://apt.llvm.org/bionic/ the package llvm-10-dev includes a LLVMExports.cmake which includes thus samples. See /data/user/lib/llvm-10/lib/cmake/llvm/LLVMExports.cmake in http://apt.llvm.org/bionic/pool/main/l/llvm-toolchain-snapshot/llvm-10-dev_10~svn372305-1~exp1%2b0~20190919071908.1206~1.gbp6f40e3_amd64.deb
When trying to use llvm-10-dev using CMake from travis (with this config https://github.com/Jiboo/wembed/blob/54e9664d615313f39e1a4325c1e7f028ce2b72db/.travis.yml), I get the error:
CMake Error at /usr/lib/llvm-10/lib/cmake/llvm/LLVMExports.cmake:1341 (message): The imported target "SampleAnalyzerPlugin" references the file "/usr/lib/llvm-10/lib/SampleAnalyzerPlugin.so" but this file does not exist. Possible reasons include: * The file was deleted, renamed, or moved to another location. * An install or uninstall procedure did not complete successfully. * The installation package was faulty and contained "/usr/lib/llvm-10/lib/cmake/llvm/LLVMExports.cmake" but not all the files it references.
I couldn't find SampleAnalyzerPlugin.so in any other packages (clang-10-examples only has sources), so I tried to replicate the problem locally, CLANG_BUILD_EXAMPLES was OFF, although the sample plugins were built and installed. Deleting /usr/local/lib/SampleAnalyzerPlugin.so replicated the travis error.
This fix looks ok to me, although I'm no CMake expert, particularly in LLVM context, and I might cure a symptom and not the cause, but with this patch if CLANG_BUILD_EXAMPLES is OFF, they don't appear in LLVMExports.cmake are not build/installed, and vice-versa if it's ON.