Just recording here that the llvm11 package currently fails to build for epel8 because of cmake issues:

+ /usr/bin/cmake -DCMAKE_C_FLAGS_RELEASE:STRING=-DNDEBUG -DCMAKE_CXX_FLAGS_RELEASE:STRING=-DNDEBUG -DCMAKE_Fortran_FLAGS_RELEASE:STRING=-DNDEBUG -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON -DCMAKE_INSTALL_PREFIX:PATH=/usr -DINCLUDE_INSTALL_DIR:PATH=/usr/include -DLIB_INSTALL_DIR:PATH=/usr/lib64 -DSYSCONF_INSTALL_DIR:PATH=/etc -DSHARE_INSTALL_PREFIX:PATH=/usr/share -DLIB_SUFFIX=64 -DBUILD_SHARED_LIBS:BOOL=ON -G Ninja -DBUILD_SHARED_LIBS:BOOL=OFF -DLLVM_PARALLEL_LINK_JOBS=1 -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_SKIP_RPATH:BOOL=ON -DLLVM_TARGETS_TO_BUILD=all -DLLVM_ENABLE_LIBCXX:BOOL=OFF -DLLVM_ENABLE_ZLIB:BOOL=ON -DLLVM_ENABLE_FFI:BOOL=ON -DLLVM_ENABLE_RTTI:BOOL=ON -DLLVM_BINUTILS_INCDIR=/usr/include -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=AVR -DLLVM_BUILD_RUNTIME:BOOL=ON -DLLVM_INCLUDE_TOOLS:BOOL=ON -DLLVM_BUILD_TOOLS:BOOL=ON -DLLVM_INCLUDE_TESTS:BOOL=ON -DLLVM_BUILD_TESTS:BOOL=ON -DLLVM_INCLUDE_EXAMPLES:BOOL=ON -DLLVM_BUILD_EXAMPLES:BOOL=OFF -DLLVM_INCLUDE_UTILS:BOOL=ON -DLLVM_INSTALL_UTILS:BOOL=OFF -DLLVM_INCLUDE_DOCS:BOOL=ON -DLLVM_BUILD_DOCS:BOOL=ON -DLLVM_ENABLE_SPHINX:BOOL=ON -DLLVM_ENABLE_DOXYGEN:BOOL=OFF -DLLVM_BUILD_LLVM_DYLIB:BOOL=ON -DLLVM_DYLIB_EXPORT_ALL:BOOL=ON -DLLVM_LINK_LLVM_DYLIB:BOOL=ON -DLLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL=ON -DLLVM_INSTALL_TOOLCHAIN_ONLY:BOOL=OFF -DSPHINX_WARNINGS_AS_ERRORS=OFF -DCMAKE_INSTALL_PREFIX=/usr/lib64/llvm11 -DLLVM_INSTALL_SPHINX_HTML_DIR=/usr/share/doc/llvm11/html -DSPHINX_EXECUTABLE=/usr/bin/sphinx-build-3
CMake Warning:
  No source or binary directory provided.  Both will be assumed to be the
  same as the current working directory, but note that this warning will
  become a fatal error in future CMake releases.
-- The C compiler identification is GNU 8.5.0
-- The CXX compiler identification is GNU 8.5.0
-- The ASM compiler identification is GNU
-- Found assembler: /usr/bin/cc
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:258 (message):
  In-source builds are not allowed.
  Please create a directory and run cmake from there, passing the path
  to this source directory as the last argument.
  This process created the file `CMakeCache.txt' and the directory
  `CMakeFiles'.
  Please delete them.
-- Configuring incomplete, errors occurred!
See also "/builddir/build/BUILD/llvm-11.1.0.src/CMakeFiles/CMakeOutput.log".