Use a specified list of languages in cmake project() command.

This allows asm files and Cxx files to be compiled with different flags
rather than treating them identically. LLVM itself has no asm files
other than tests, but this setting is inherited by the compiler-rt
project (unless compiled standalone), which does have asm files.

Differential Revision: http://reviews.llvm.org/D10707

llvm-svn: 243419