add a dependency on terminfo library if llvm uses it

[jeremi.piotrowski]

Summary

Ncurses related symbols can either all be found in libnurses or split between
libncurses and libtinfo. The main LLVM cmake scripts look for the setupterm
symbol and stores the library that has it in TERMINFO_LIBS. This covers the
split and unified ncurses case. LLDB uses symbols that can end up in libtinfo so
this library should be pulled in if it is found.

There is still an exotic case left where LLDB is configured with
-DLLDB_DISABLE_CURSES=NO and LLVM with -DLLVM_ENABLE_TERMINFO=NO but
misconfigurations will always be possible. Possibly a diagnostic could be added
for that.

This fixes bug 24693 (https://llvm.org/bugs/show_bug.cgi?id=24693).

[zturner]

Looks fine to me, but as a nitpick, I would suggest combining the nested if
into a single if with an AND clause.

[jeremi.piotrowski]

• combine nested if conditions with and as suggested by zturner
  
  and remove condtition from endif as that seems to be the convention.

[zturner]

Looks fine, do you have commit access? If so feel free to commit
whenever. Otherwise I can do it for you tomorrow

[jeremi.piotrowski]

I do not have commit access, so if you could do it for me that would be great.

[zturner]

Sorry this took so long, I forgot about it. It has been committed in r247842.

cmake/LLDBDependencies.cmake

 
 set(LLDB_SYSTEM_LIBS)
 if (NOT CMAKE_SYSTEM_NAME MATCHES "Windows" AND NOT __ANDROID_NDK__)
   if (NOT LLDB_DISABLE_LIBEDIT)
     list(APPEND LLDB_SYSTEM_LIBS edit)
   endif()
   if (NOT LLDB_DISABLE_CURSES)
     list(APPEND LLDB_SYSTEM_LIBS panel ncurses)
+    if(LLVM_ENABLE_TERMINFO AND HAVE_TERMINFO)
+      list(APPEND LLDB_SYSTEM_LIBS ${TERMINFO_LIBS})
+    endif()
   endif()
 endif()
 # On FreeBSD backtrace() is provided by libexecinfo, not libc.
 if (CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
   list(APPEND LLDB_SYSTEM_LIBS execinfo)
 endif()
 
 if (NOT LLDB_DISABLE_PYTHON AND NOT LLVM_BUILD_STATIC)