It seems that due to recent changes in glibc, defining
_POSIX_ in a C source file that includes math.h will cause
parsing of math.h to fail.  A minimal example:


#define _POSIX_

#include <stdio.h>
#include <math.h>

int main()
{
  printf("y = %g\n", sin(1.5));
  return 0;
}


If I compile this via

    cc -Wall -lm foo.c -o foo

I get the error message

    In file included from foo.c:4:
    /usr/include/math.h:241: parse error before `,'

But if I delete the line #define _POSIX_, this code compiles
and runs.

At a glance, I suspect that _ISOC_ on line 242 of
/usr/include/math.h is not always defined.

I'm running RH 6.0 on a Pentium with a kernel built from the
2.2.11-1 sources.  glibc and glibc-devel are version 2.1.2-4
from rawhide.