Findzstd.cmake: string sub-command REGEX, mode REPLACE: regex "$" matched an empty string. #83802
Description
When using find_package(llvm) on windows we get:
CMake Error at D:/bld/cppinterop_1709495262007/_h_env/Library/lib/cmake/llvm/Findzstd.cmake:39 (string):
2024-03-03T19:54:48.3232894Z string sub-command REGEX, mode REPLACE: regex "$" matched an empty string.
2024-03-03T19:54:48.3233394Z Call Stack (most recent call first):
2024-03-03T19:54:48.3233750Z D:/bld/cppinterop_1709495262007/_h_env/Library/lib/cmake/llvm/LLVMConfig.cmake:278 (find_package)
2024-03-03T19:54:48.3234068Z CMakeLists.txt:121 (find_package)
Our diagnosis is that find_package(LLVM REQUIRED CONFIG) triggers LLVMConfig.cmake to call find_package(zstd). In the MSVC branch we use string(REGEX REPLACE "${CMAKE_INSTALL_LIBDIR}$" "${CMAKE_INSTALL_BINDIR}" zstd_DIRNAME "${zstd_DIRNAME}"), however, CMAKE_INSTALL_LIBDIR is not defined yet and we error out:
llvm-project/llvm/cmake/modules/Findzstd.cmake
Lines 36 to 47 in da5966e
Adding include(GNUInstallDirs) which defines CMAKE_INSTALL_LIBDIR in the calling cmake fixes the problem but it's difficult to debug and and far from optimal.