Description of problem:
The following program can be compiled successfully, unless both -O (or -O2 or -O3) and -D_FORTIFY_SOURCE (or -D_FORTIFY_SOURCE=2) are specified:

int main() {
#include <unistd.h>
  return 0;
}

With both optimization and source fortification turned on, gcc reports:

In file included from /usr/include/unistd.h:1100,
                 from test.c:2:
/usr/include/bits/unistd.h: In function 'main':
/usr/include/bits/unistd.h:36: error: nested function 'read' declared 'extern'
/usr/include/bits/unistd.h:35: error: static declaration of 'read' follows non-static declaration
/usr/include/unistd.h:327: error: previous declaration of 'read' was here

...

That is followed by identical complaints about readlink, getcwd, getwd, confstr, getgroups, etc.

Version-Release number of selected component (if applicable):
glibc-headers-2.8-8.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Copy the code above into test.c
2. gcc -D_FORTIFY_SOURCE -o test test.c: the compile succeeds
3. gcc -O -o test test.c: the compile succeeds
4. gcc -O -D_FORTIFY_SOURCE -o test test.c: the compile fails
  
Actual results:
Compilation fails.

Expected results:
Compilation succeeds.

Additional info:
This is the cause of a GCL build failure.  I can work around it for now, but it would be nice to get this fixed.