libpng: upgrade 1.6.42 -> 1.6.43

libpng: upgrade 1.6.42 -> 1.6.43

Changelog:
===========
-Fixed the row width check in png_check_IHDR().
-Added eXIf chunk support to the push-mode reader in pngpread.c.
-Added contrib/pngexif for the benefit of the users who would like
 to inspect the content of eXIf chunks.
-Added contrib/conftest/basic.dfa, a basic build-time configuration.
-Fixed a preprocessor condition in pngread.c that broke build-time
 configurations like contrib/conftest/pngcp.dfa.
-Added CMake build support for LoongArch LSX.
-Fixed a CMake build error that occurred under a peculiar state of the
 dependency tree. This was a regression introduced in libpng-1.6.41.
-Marked the installed libpng headers as system headers in CMake.
-Updated the build support for RISCOS.
-Updated the makefiles to allow cross-platform builds to initialize
 conventional make variables like AR and ARFLAGS.
-Added various improvements to the CI scripts in areas like version
  consistency verification and text linting.
Added version consistency verification to pngtest.c also.

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>