Fix ncurses/zlib in LLVM_SYSTEM_LIBS for Windows GNU

[haampie]

Summary

For the Windows GNU platform, CMAKE_FIND_LIBRARY_PREFIXES is a list containing an empty string, which ended up in a regex capturing group, which is invalid in CMake's regex engine. With this change, we get the following:

set(CMAKE_FIND_LIBRARY_PREFIXES "lib" "")
set(CMAKE_FIND_LIBRARY_SUFFIXES ".dll.a" ".a" ".lib")
get_system_libname(path/to/libz.dll.a zlib)
message("${zlib}")

outputs z, as expected.

[haampie]

@mati865 can you test this on your platform? You only have to run cmake ../llvm and check whether tools/llvm-config/BuildVariables.inc: has a proper #define LLVM_SYSTEM_LIBS "-lrt -ldl -lpthread -lm -lz -ltinfo"

[mati865]

Thank you, now it works as expected:

$ cat tools/llvm-config/BuildVariables.inc | grep LLVM_SYSTEM_LIBS
#define LLVM_SYSTEM_LIBS "-lpsapi -lshell32 -lole32 -luuid -ladvapi32 -lz"

[hans]

This broke Chromium's clang packaging:
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8871016556723646144/+/steps/package_clang/0/stdout

CMake Error at lib/Support/CMakeLists.txt:13 (string):

string sub-command REGEX, mode REPLACE: regex "^()" matched an empty
string.

Call Stack (most recent call first):

lib/Support/CMakeLists.txt:223 (get_system_libname)

I've reverted in 6da4f1199e7c3129f6e2ef7a24a2c75e386be32d

llvm/lib/Support/CMakeLists.txt

 if(LLVM_ENABLE_ZLIB)
   set(imported_libs ZLIB::ZLIB)
 endif()
 
 function(get_system_libname libpath libname)
   get_filename_component(libpath ${libpath} NAME)
-  if( CMAKE_FIND_LIBRARY_PREFIXES )
-    string(REPLACE ";" "|" PREFIXES "${CMAKE_FIND_LIBRARY_PREFIXES}")
-    string(REGEX REPLACE "^(${PREFIXES})" "" libpath ${libpath})
-  endif()
-  if( CMAKE_FIND_LIBRARY_SUFFIXES )
-    string(REPLACE ";" "|" SUFFIXES "${CMAKE_FIND_LIBRARY_SUFFIXES}")
-    string(REGEX REPLACE "(${SUFFIXES})$" "" libpath ${libpath})
-  endif()
+  set(prefixes ${CMAKE_FIND_LIBRARY_PREFIXES})
+  set(suffixes ${CMAKE_FIND_LIBRARY_SUFFIXES})
+  list(FILTER prefixes EXCLUDE REGEX "^\\s*$")
+  list(FILTER suffixes EXCLUDE REGEX "^\\s*$")
+  string(REPLACE ";" "|" prefixes "${prefixes}")
+  string(REPLACE ";" "|" suffixes "${suffixes}")
+  string(REGEX REPLACE "^(${prefixes})" "" libpath ${libpath})
+  string(REGEX REPLACE "(${suffixes})$" "" libpath ${libpath})
   set(${libname} "${libpath}" PARENT_SCOPE)
 endfunction()
 
 if( MSVC OR MINGW )
   # libuuid required for FOLDERID_Profile usage in lib/Support/Windows/Path.inc.
   # advapi32 required for CryptAcquireContextW in lib/Support/Windows/Path.inc.
   set(system_libs ${system_libs} psapi shell32 ole32 uuid advapi32)
 elseif( CMAKE_HOST_UNIX )