[cmake] Explicitly link dependency libraries in the Host library

[mgorny]

Summary

Add explicit linkage to the necessary system libraries in the Host
library. Otherwise, the library fails to build with -Wl,--as-needed.
The system libraries ended up being listed on the linker command-line
before the static libraries needing them, resulting in --as-needed
stripping them.

Listing the dependent libraries explicitly is the canonical way of
declaring libraries in CMake. It guarantees that the system library
dependencies will be correctly propagated to reverse dependencies.

The code used to link libraries reuses existing EXTRA_LIBS variable,
copying code from other parts of LLDB. We might eventually remove
the direct use of system libraries in the programs; however, I would
prefer if we focused on fixing the build regressions in 5.0 branch
first, and went further after the release.

[zturner]

source/Host/CMakeLists.txt

166–168

Even if libxml is found, that doesn't mean the build is configured to use it, does it? Correct me if I'm wrong. if "libxml exists" is the same as "i want to use libxml" then this seems fine.

[mgorny]

source/Host/CMakeLists.txt

166–168

Strictly speaking, it's not the same. However, LLDB build system does not provide an explicit option to disable building with libxml2 support, so it's not a regression. It's exactly the same logic as used in other parts of LLDB. If you want, I can look into adding an additional conditional for it in a followup patch. However, I'm not sure if it should be applied to APPLE as well or not since the presumption of libxml2 is unconditional there right now.

source/Host/CMakeLists.txt

execute_process(
     RESULT_VARIABLE get_libdir_status
     OUTPUT_VARIABLE relative_libdir
     )
   if (get_libdir_status EQUAL 0)
     add_definitions(-DLLDB_PYTHON_RELATIVE_LIBDIR="${relative_libdir}")
   endif()
 endif()
 
+set(EXTRA_LIBS)
 if (CMAKE_SYSTEM_NAME MATCHES "NetBSD")
- set(EXTRA_LIBS kvm)
-endif ()
+  list(APPEND EXTRA_LIBS kvm)
+endif ()
+if (APPLE)
+  list(APPEND EXTRA_LIBS xml2)
+else ()
+  if (LIBXML2_FOUND)
+    list(APPEND EXTRA_LIBS ${LIBXML2_LIBRARIES})
+  endif()
+endif ()
+if (HAVE_LIBDL)
+  list(APPEND EXTRA_LIBS ${CMAKE_DL_LIBS})
+endif()
+if (NOT LLDB_DISABLE_LIBEDIT)
+  list(APPEND EXTRA_LIBS edit)
+endif()
 
 add_lldb_library(lldbHost
   ${HOST_SOURCES}
   
   LINK_LIBS
     lldbCore
     lldbInterpreter
     lldbSymbol
     lldbTarget
     lldbUtility
     ${LLDB_PLUGINS}
     ${EXTRA_LIBS}
   
   LINK_COMPONENTS
     Support
   )