Add check for BSD when setting LIB_NAMES for GNU ld

[ararslan]

Summary

FreeBSD (as well as DragonFly BSD) uses GNU ld for linking, but is not captured in the conditional on Linux or MinGW when setting LIB_NAMES. This causes a shared library with no symbols on FreeBSD. This patch simply adds a check for whether the CMake system name is FreeBSD or DragonFly in addition to the existing checks for Linux and MinGW.

This patch is based on that used by the FreeBSD LLVM 3.9 port, revision 426189. The majority of the diff is by Koop Mast (kwm). Alex Arslan (ararslan) updated it for use on the current LLVM trunk.

[ararslan]

Thanks for taking a look at this, @axw. Is there anything else that needs to happen before this can be merged?

[axw]

In D28215#710769, @ararslan wrote:

Thanks for taking a look at this, @axw. Is there anything else that needs to happen before this can be merged?

Nope, sorry - I've committed it now.

llvm/trunk/tools/llvm-shlib/CMakeLists.txt

 if(LLVM_DYLIB_EXPORTED_SYMBOL_FILE)
   set(LLVM_EXPORTED_SYMBOL_FILE ${LLVM_DYLIB_EXPORTED_SYMBOL_FILE})
   add_custom_target(libLLVMExports DEPENDS ${LLVM_EXPORTED_SYMBOL_FILE})
 endif()
 
 add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB SONAME ${SOURCES})
 
 list(REMOVE_DUPLICATES LIB_NAMES)
-if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" OR MINGW) # FIXME: It should be "GNU ld for elf"
+if(("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux") OR (MINGW) OR ("${CMAKE_SYSTEM_NAME}" STREQUAL "FreeBSD") OR ("${CMAKE_SYSTEM_NAME}" STREQUAL "DragonFly")) # FIXME: It should be "GNU ld for elf"
   # GNU ld doesn't resolve symbols in the version script.
   set(LIB_NAMES -Wl,--whole-archive ${LIB_NAMES} -Wl,--no-whole-archive)
 elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")
   set(LIB_NAMES -Wl,-all_load ${LIB_NAMES})
 endif()
 
 target_link_libraries(LLVM PRIVATE ${LIB_NAMES})