Make COMPILER_VERSION more compatible with clang 3.8 trunk.

"clang version 3.8.0 (trunk 256945) (based on LLVM 3.8.0svn)" was giving
"38 38" was a result. Now duplicates for fmake are trimmed and only the first
version found is used for bmake using its :tW.

With hat: portmgr
In collaboration with: dim