At the moment the ECF_* flags for a gimple call to a built-in
function are derived from the function decl, which in turn is
derived from the global command-line options.  So if the compiler
is run with -fno-math-errno, we always assume functions don't set
errno, regardless of local optimization options.  Similarly if the
compiler is run with -fmath-errno, we always assume functions set errno.

This shows up in gcc.dg/lto/20110201-1_0.c, where we compile
the file with -O0 and use -O2 -ffast-math for a specific function.
-O2 -ffast-math is enough for us to convert cabs to sqrt as hoped,
but because of the global -fmath-errno setting, we assume that the
call to sqrt is not pure or const and create vops for it.  This makes
it appear to the gimple code that a simple sqrt optab isn't enough.

Later patches move more decisions about maths functions to gimple
and think that in this case we should use:

        y = sqrt (x);
        if (!(x >= 0))
            sqrt (x); // to set errno.

This is being tracked as PR68235.  For now the patch adds
-fno-math-errno to the dg-options for this test.

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/testsuite/
	PR tree-optimization/68235
	* gcc.dg/lto/20110201-1_0.c: Add -fno-math-errno.

From-SVN: r229917