What is wrong with building the embedded Linux kernel?

Question

linux

Gentlemen, I ran into a rather specific problem: I'm trying to build a Linux kernel for one piece of iron using buildroot. During the build process I get the following error:

CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  CC      mm/ksm.o
  LD      sound/built-in.o
  CC      kernel/smp.o
In file included from include/linux/linkage.h:6:0,
                 from include/linux/preempt.h:9,
                 from include/linux/spinlock.h:50,
                 from include/linux/mmzone.h:7,
                 from include/linux/gfp.h:5,
                 from include/linux/mm.h:9,
                 from mm/ksm.c:18:
include/linux/export.h:57:2: error: expected ‘,’ or ‘;’ before ‘extern’
  extern typeof(sym) sym;     \

In the export.h file, this fragment is used in a macro:

/* For every exported symbol, place a struct in the __ksymtab section */
#define __EXPORT_SYMBOL(sym, sec)				\
  extern typeof(sym) sym;					\
  __CRC_SYMBOL(sym, sec)					\
  static const char __kstrtab_##sym[]			\
  __attribute__((section("__ksymtab_strings"), aligned(1))) \
  = VMLINUX_SYMBOL_STR(sym);				\
  extern const struct kernel_symbol __ksymtab_##sym;	\
  __visible const struct kernel_symbol __ksymtab_##sym	\
  __used							\
  __attribute__((section("___ksymtab" sec "+" #sym), unused))	\
  = { (unsigned long)&sym, __kstrtab_##sym }

I don't see anything criminal in it. Moreover, it is a standard kernel macro. What is the build error?