Add an option to disable libedit

[yuyichao]

Summary

This should provide the function similar to --disable-libedit with the autotools build system, which seems to be missing from the commit (r200595) that adds this.

[yuyichao]

Ping

[beanz]

LGTM.

CMakeLists.txt

 set(FFI_LIBRARY_DIR "" CACHE PATH "Additional directory, where CMake should search for libffi.so")
 set(FFI_INCLUDE_DIR "" CACHE PATH "Additional directory, where CMake should search for ffi.h or ffi/ffi.h")
 
 set(LLVM_TARGET_ARCH "host"
   CACHE STRING "Set target to use for LLVM JIT or use \"host\" for automatic detection.")
 
 option(LLVM_ENABLE_TERMINFO "Use terminfo database if available." ON)
 
+option(LLVM_ENABLE_LIBEDIT "Use libedit if available." ON)
+
 option(LLVM_ENABLE_THREADS "Use threads if available." ON)
 
 option(LLVM_ENABLE_ZLIB "Use zlib for compression/decompression if available." ON)
 
 if( LLVM_TARGETS_TO_BUILD STREQUAL "all" )
   set( LLVM_TARGETS_TO_BUILD ${LLVM_ALL_TARGETS} )
 endif()
 

cmake/config-ix.cmake

 # like strlen, leading to false positives.
 if( NOT PURE_WINDOWS AND NOT LLVM_USE_SANITIZER MATCHES "Memory.*")
   if (LLVM_ENABLE_ZLIB)
     check_library_exists(z compress2 "" HAVE_LIBZ)
   else()
     set(HAVE_LIBZ 0)
   endif()
   # Skip libedit if using ASan as it contains memory leaks.
-  if (HAVE_HISTEDIT_H AND NOT LLVM_USE_SANITIZER MATCHES ".*Address.*")
+  if (LLVM_ENABLE_LIBEDIT AND HAVE_HISTEDIT_H AND NOT LLVM_USE_SANITIZER MATCHES ".*Address.*")
     check_library_exists(edit el_init "" HAVE_LIBEDIT)
+  else()
+    set(HAVE_LIBEDIT 0)
   endif()
   if(LLVM_ENABLE_TERMINFO)
     set(HAVE_TERMINFO 0)
     foreach(library tinfo terminfo curses ncurses ncursesw)
       string(TOUPPER ${library} library_suffix)
       check_library_exists(${library} setupterm "" HAVE_TERMINFO_${library_suffix})
       if(HAVE_TERMINFO_${library_suffix})
         set(HAVE_TERMINFO 1)