title: Compile gcc6.4.0 using gcc8.1.1
body: <p>I tried to install gcc6.4.0 in Fedora28, while something wrong happened as following.</p>
  
  <pre><code>In file included from ../.././libgcc/unwind-dw2.c:401:0:
  ./md-unwind-support.h: In function ‘x86_64_fallback_frame_state’:
  ./md-unwind-support.h:65:47: error: dereferencing pointer to incomplete type ‘struct ucontex_t’
         sc = (struct sigcontext *) (void *) &amp;uc_-&gt;uc_mcontext;
                                                 ^~
  </code></pre>
  
  <p>And at the end the message is here:</p>
  
  <pre><code>make[3]: *** [../.././libgcc/shared-object.mk:14: unwind-dw2.o] Error 1
  make[3]: *** Waiting for unfinished jobs....
  make[3]: Leaving directory '/home/rx/program/gcc-6.4.0/x86_64-pc-linux-gnu/libgcc'
  make[2]: *** [Makefile:17378: all-stage1-target-libgcc] Error 2
  make[2]: Leaving directory '/home/rx/program/gcc-6.4.0'
  make[1]: *** [Makefile:23677: stage1-bubble] Error 2
  make[1]: Leaving directory '/home/rx/program/gcc-6.4.0'
  make: *** [Makefile:914: all] Error 2
  </code></pre>
  
  <p>I have try <a href="https://stackoverflow.com/questions/46999900/how-to-compile-gcc-6-4-0-with-gcc-7-2-in-archlinux">the previous solution</a>, but it still failed.</p>
  
  <p>Am I missing something? Thank you!</p>