[llvm] [cmake] Remove obsolete /usr/local hack for *BSD

[mgorny]

Summary

Remove the hack adding /usr/local paths on FreeBSD and DragonFlyBSD.
It does not seem to be necessary today, and it breaks cross builds.

[theraven]

This patch certainly looks correct for fixing the symptom, but I'm somewhat concerned that the original logic was incorrect anyway. I believe CMake's FindLibrary and FindPackage work correctly with things installed in /usr/local on FreeBSD, so I don't know why we need these.

[arichardson]

What happens if you just drop this block unconditionally?

[mgorny]

In D94491#2492663, @arichardson wrote:

What happens if you just drop this block unconditionally?

It seems to find libxml2 correctly. However, rebuilding everything will take a while. I'll report back when I confirm that everything built without issues.

[mgorny]

Trying to add people responsible for the DragonFly part.

[mgorny]

I can confirm that it builds fine without that block and that there are no changes in CMakeCache.txt.

[arichardson]

In D94491#2492705, @mgorny wrote:

I can confirm that it builds fine without that block and that there are no changes in CMakeCache.txt.

That sounds good. My guess would be that this was "needed" at some point in the past because certain targets weren't adding things like ${LIBXML2_INCLUDE_DIRS} with target_include_directories, etc.

[theraven]

Patches that just remove code without breaking functionality are my favourite kind!

[mgorny]

Change the patch to remove the hack entirely.

[theraven]

Great!

llvm/CMakeLists.txt

if(LLVM_USE_HOST_TOOLS)
   include(CrossCompile)
   llvm_create_cross_target(LLVM NATIVE "" Release)
 endif(LLVM_USE_HOST_TOOLS)
 if(LLVM_TARGET_IS_CROSSCOMPILE_HOST)
 # Dummy use to avoid CMake Warning: Manually-specified variables were not used
 # (this is a variable that CrossCompile sets on recursive invocations)
 endif()
 
-if(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)")
+if(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)" AND NOT CMAKE_CROSSCOMPILING)
   # On FreeBSD, /usr/local/* is not used by default. In order to build LLVM
   # with libxml2, iconv.h, etc., we must add /usr/local paths.
   include_directories(SYSTEM "/usr/local/include")
   link_directories("/usr/local/lib")
-endif(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)")
+endif(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)" AND NOT CMAKE_CROSSCOMPILING)
 
 if( ${CMAKE_SYSTEM_NAME} MATCHES SunOS )
    # special hack for Solaris to handle crazy system sys/regset.h
    include_directories("${LLVM_MAIN_INCLUDE_DIR}/llvm/Support/Solaris")
 endif( ${CMAKE_SYSTEM_NAME} MATCHES SunOS )
 
 # Make sure we don't get -rdynamic in every binary. For those that need it,
 # use export_executable_symbols(target).