Make the triple an explicit argument of FindTargetProgramPath.

Preserve the original triple in the NetBSD toolchain when using -m32 or
-m64 and the resulting effective target is different from the triple it
started with. This allows -m32 to use the same assembler/linking in
cross-compiling mode and avoids confusion about passing down target
specific flags in that case like --32.

llvm-svn: 131404