uname -m doesn't return useful information on Solarish systems (for example, on this 64-bit vm, it returns 'i86pc' which is also the same value if it were a 32-bit vm). The isainfo command will return amd64/i386 (for x86, sparc/sparcv9 if SPARC is ever supported) depending on the host platform.
Commit pushed to master at https://github.com/D-Programming-Language/druntime https://github.com/D-Programming-Language/druntime/commit/aa5e8e4c8c9f010680fd3b543f62df3f0af86fc2 Merge pull request #850 from jasonbking/isainfo Fix issue 12975 - Should use isainfo on Solaris systems to determine model