Separate construction of bi-arch path suffix from construction of

multi-library path suffix.

The code calculates MIPS toolchain specific multi-lib path suffixes like
mips16/soft-float/el is moved to the separate function
findMultiLibSuffix(). This function called during GCC installation
detection and result is stored for the future using.

The patch reviewed by Rafael Espindola.
http://llvm-reviews.chandlerc.com/D1738

llvm-svn: 191612