[libpng16] Fixed race conditions in parallel make builds. With higher degrees

of parallelism during 'make' the use of the same temporary file names such
as 'dfn*' can result in a race where a temporary file from one arm of the
build is deleted or overwritten in another arm.  This changes the
temporary files for suffix rules to always use $* and ensures that the
non-suffix rules use unique file names.
4 files changed