Build fails on importing gnulib

[ayush goel]

Build fails on including gnulib header files in the include path

In file included from insn-modes.c:5:
In file included from /Users/ayushgoel/gsoc/src/gcc/system.h:294:
../gnulib/import/unistd.h:135:3: error: "Please include config.h first."
 #error "Please include config.h first."
  ^
../gnulib/import/unistd.h:137:1: error: unknown type name '_GL_INLINE_HEADER_BEGIN'
_GL_INLINE_HEADER_BEGIN

I’m assuming after the newer version of gnulib it is required to include config.h before the system headers.
However config.h has already been included before system.h in all such files. 

Is this due to some variable like HAVE_CONFIG_H being set?

--  
Thanks,  
Ayush Goel