[build] Check for unicode functions in libedit

Some versions of libedit may have histedit.h but not the Unicode
functions. Explicitly check for the Unicode functions in the found
libedit to ensure the check is accurate.

I considered making this a component of the LibEdit package in our find
module, but CMake's documentation [1] says "Packages that find multiple
semi-independent parts (like bundles of libraries) should search for the
components...", and the "multiple semi-independent parts" definitely
isn't the case here; we're just interested in determining if the found
library supports a particular feature.

[1] https://cmake.org/cmake/help/v3.16/manual/cmake-developer.7.html#find-modules

Author: smeenai

CMakeLists.txt

@@ -930,6 +930,19 @@ else()
   find_package(LibEdit)
 endif()
 
+if(LibEdit_FOUND)
+  cmake_push_check_state()
+  list(APPEND CMAKE_REQUIRED_INCLUDES ${LibEdit_INCLUDE_DIRS})
+  list(APPEND CMAKE_REQUIRED_LIBRARIES ${LibEdit_LIBRARIES})
+  check_symbol_exists(el_wgets "histedit.h" HAVE_EL_WGETS)
+  if(HAVE_EL_WGETS)
+    set(LibEdit_HAS_UNICODE YES)
+  else()
+    set(LibEdit_HAS_UNICODE NO)
+  endif()
+  cmake_pop_check_state()
+endif()
+
 check_symbol_exists(wait4 "sys/wait.h" HAVE_WAIT4)
 
 check_symbol_exists(proc_pid_rusage "libproc.h" HAVE_PROC_PID_RUSAGE)

lib/Immediate/CMakeLists.txt

@@ -12,7 +12,7 @@ target_link_libraries(swiftImmediate PRIVATE
   swiftIRGen
   swiftSILGen
   swiftSILOptimizer)
-if(LibEdit_FOUND)
+if(LibEdit_FOUND AND LibEdit_HAS_UNICODE)
   target_compile_definitions(swiftImmediate PRIVATE
     HAVE_LIBEDIT)
   target_link_libraries(swiftImmediate PRIVATE

tools/SourceKit/tools/CMakeLists.txt

@@ -6,7 +6,7 @@ include_directories(
 
 add_swift_lib_subdirectory(sourcekitd)
 add_swift_tool_subdirectory(sourcekitd-test)
-if(LibEdit_FOUND)
+if(LibEdit_FOUND AND LibEdit_HAS_UNICODE)
   add_swift_tool_subdirectory(sourcekitd-repl)
 endif()
 add_swift_tool_subdirectory(complete-test)