Compute Solaris device numbers without libc's private helpers.

Related Mozilla import:
  imports/260513.patch
  Petr Sumbera, "Bug 2039309 follow-up - avoid Solaris major/minor
  relocations in libxul", Mon May 18 2026.

The libxul version script gives unlisted symbols local binding, so the Solaris
major() and minor() macros leave unsatisfied references to their __major and
__minor implementations.  The public mkdev constants describe the device
layout and avoid adding private libc implementation symbols to libxul's ABI.

--- firefox-153.0/dom/media/platforms/ffmpeg/FFmpegVulkanVideoDecoder.cpp
+++ firefox-153.0/dom/media/platforms/ffmpeg/FFmpegVulkanVideoDecoder.cpp
@@ -488,8 +488,17 @@ bool FFmpegVideoDecoder<LIBAV_VER>::FFmp
   if (!aRendererNode.IsEmpty()) {
     struct stat st = {};
     if (stat(aRendererNode.get(), &st) == 0) {
+#      if defined(XP_SOLARIS) || defined(__sun)
+      // Avoid the Solaris major()/minor() libc helpers.  libxul's version
+      // script gives unlisted symbols local binding, so references to their
+      // __major/__minor implementations cannot be satisfied at link time.
+      rendererDrmMajor =
+          (static_cast<uint64_t>(st.st_rdev) >> NBITSMINOR) & MAXMAJ;
+      rendererDrmMinor = static_cast<uint64_t>(st.st_rdev) & MAXMIN;
+#      else
       rendererDrmMajor = major(st.st_rdev);
       rendererDrmMinor = minor(st.st_rdev);
+#      endif
       FFMPEGV_LOG("Renderer device from GPU: {} (major={}, minor={})",
                   aRendererNode.get(), rendererDrmMajor, rendererDrmMinor);
     } else {