archivers/libdeflate: update the port to version 1.15

• The build system had been switched to CMake, adjust the Makefile accordingly and convert outgrown PLIST_FILES into static pkg-plist
• Backport one upstream commit for the sake of consistency, so unit tests reflect on release binaries (it also happens to inadvertently inhibit detection of futimes(2), which is deprecated interface as it does not provide nanosecond accuracy, so it's probably okay)
• Do not pass "-O2 -DNDEBUG" on release CFLAGS: -O2 is redundant and NDEBUG is not actually used anywhere in the library source code

PR: 268519