macOS: Remove obsolete -single_module flag.

Thanks to dundargoc.

(cherry picked from commit 97813fb)

The aforementioned flag is the default since Xcode 2.2 [1].
This patch removes this flag to avoid warnings for modern Xcode
versions at the linking stage.

[1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1743539#c1

Sergey Kaplun:
* added the description for the problem

Part of tarantool/tarantool#11691

Author: Mike Pall

cmake/SetTargetFlags.cmake

@@ -47,7 +47,7 @@ if(LUAJIT_ARCH STREQUAL "x86")
 endif()
 
 if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
-  AppendFlags(TARGET_SHARED_FLAGS -single_module -undefined dynamic_lookup)
+  AppendFlags(TARGET_SHARED_FLAGS -undefined dynamic_lookup)
 else() # Linux and FreeBSD.
   AppendFlags(TARGET_BIN_FLAGS -Wl,-E)
   list(APPEND TARGET_LIBS dl)

src/Makefile.original

@@ -329,13 +329,13 @@ ifeq (Darwin,$(TARGET_SYS))
   endif
   TARGET_STRIP+= -x
   TARGET_XCFLAGS+= -DLUAJIT_UNWIND_EXTERNAL
-  TARGET_XSHLDFLAGS= -dynamiclib -single_module -undefined dynamic_lookup -fPIC
+  TARGET_XSHLDFLAGS= -dynamiclib -undefined dynamic_lookup -fPIC
   TARGET_DYNXLDOPTS=
   TARGET_XSHLDFLAGS+= -install_name $(TARGET_DYLIBPATH) -compatibility_version $(MAJVER).$(MINVER) -current_version $(MAJVER).$(MINVER).$(RELVER)
 else
 ifeq (iOS,$(TARGET_SYS))
   TARGET_STRIP+= -x
-  TARGET_XSHLDFLAGS= -dynamiclib -single_module -undefined dynamic_lookup -fPIC
+  TARGET_XSHLDFLAGS= -dynamiclib -undefined dynamic_lookup -fPIC
   TARGET_DYNXLDOPTS=
   TARGET_XSHLDFLAGS+= -install_name $(TARGET_DYLIBPATH) -compatibility_version $(MAJVER).$(MINVER) -current_version $(MAJVER).$(MINVER).$(RELVER)
   ifeq (arm64,$(TARGET_LJARCH))