Fix local variable hides function parameter for GLSL ES 1.0

Fix local variable hides function parameter for GLSL ES 1.0

GLSL ES 1.0 specifies that "a function body has a scope nested inside
the function’s definition". For GLSL ES 3.0, they form a single scope.
Both specs use the compound_statement_no_new_scope rule. This change
respects that while supporting both behaviors. It does not impact legacy
content since it makes things more permissive.

Change-Id: Ica40fbf4d24d441ca2288fe5d43c288161e16b89
Reviewed-on: https://swiftshader-review.googlesource.com/5055
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>