glsl: Use ir_var_temporary when generating inline functions.

glsl: Use ir_var_temporary when generating inline functions.

We were using ir_var_auto for the inlined function parameter variables,
which is wrong, as it suggests that those are real variables declared
by the program.

Normally this doesn't matter.  However, if you called built-ins at
global scope, it would pollute the global variable namespace with
these new parameter temporaries.  If the shader already had variables
with those names, the linker might see contradictory global variable
declarations and raise an error.

Making them temporaries indicates that these are just things generated
by the compiler internally.  This avoids confusing the linker.

Fixes a new Piglit test: glsl-fs-multiple-builtins.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99154
Reported-by: Niels Ole Salscheider <niels_ole@salscheider-online.de>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>