[cmake] Fix zlib library detection

[labath]

Summary

A couple of people were broken by the previous zlib patch. It turned out
this was because I used find_libraries for searching for the z library.
This returns absolute paths, and when these paths made it into
llvm-config, it made it produce nonsensical flags for the --system-libs
output. To fix this, I hand-roll a search for the library in the same
way that we search for the terminfo library a couple of lines below.

This is a bit less flexible than the find_library option, as it does not
allow the user to specify the path to the library at configure time
(which is important on windows, as zlib is unlikely to be found in any
of the standard places cmake searches), but I was able to guide the
build to find it with appropriate values of LIB and INCLUDE environment
variables.

[compnerd]

cmake/config-ix.cmake

143

It might be nicer if this was out-of-lined.

[labath]

cmake/config-ix.cmake

143

I think that makes sense only if that code is made more generic so it can be re-used. I could make a patch that makes a more generic version of this, and then use that to implement the search for zlib and terminfo. What do you think?

cmake/config-ix.cmake

if(HAVE_LIBPTHREAD)
   set(THREADS_HAVE_PTHREAD_ARG Off)
   find_package(Threads REQUIRED)
   set(LLVM_PTHREAD_LIB ${CMAKE_THREAD_LIBS_INIT})
 endif()
 
 # Don't look for these libraries if we're using MSan, since uninstrumented third
 # party code may call MSan interceptors like strlen, leading to false positives.
 if(NOT LLVM_USE_SANITIZER MATCHES "Memory.*")
-  find_library(ZLIB_LIBRARY_PATH NAMES z zlib)
-  if (LLVM_ENABLE_ZLIB AND ZLIB_LIBRARY_PATH)
-    check_library_exists(${ZLIB_LIBRARY_PATH} compress2 "" HAVE_LIBZ)
-  else()
-    set(HAVE_LIBZ 0)
+  if(LLVM_ENABLE_ZLIB)
+    foreach(library z zlib_static zlib)
+      string(TOUPPER ${library} library_suffix)
+      check_library_exists(${library} compress2 "" HAVE_LIBZ_${library_suffix})
+      if(HAVE_LIBZ_${library_suffix})
+        set(HAVE_LIBZ 1)
+        set(ZLIB_LIBRARIES "${library}")
+        break()
+      endif()
+    endforeach()
   endif()
 
   # Don't look for these libraries on Windows.
   if (NOT PURE_WINDOWS)
     # Skip libedit if using ASan as it contains memory leaks.
     if (LLVM_ENABLE_LIBEDIT AND HAVE_HISTEDIT_H AND NOT LLVM_USE_SANITIZER MATCHES ".*Address.*")
       check_library_exists(edit el_init "" HAVE_LIBEDIT)
     else()

lib/Support/CMakeLists.txt

 set(system_libs)
 if ( LLVM_ENABLE_ZLIB AND HAVE_LIBZ )
-  set(system_libs ${system_libs} ${ZLIB_LIBRARY_PATH})
+  set(system_libs ${system_libs} ${ZLIB_LIBRARIES})
 endif()
 if( MSVC OR MINGW )
   # libuuid required for FOLDERID_Profile usage in lib/Support/Windows/Path.inc.
   set(system_libs ${system_libs} psapi shell32 ole32 uuid)
 elseif( CMAKE_HOST_UNIX )
   if( HAVE_LIBRT )
     set(system_libs ${system_libs} rt)
   endif()